Q.1 Which of the following processes primarily drives the corrosion of metallic biomaterials in physiological environments?
Electrochemical oxidation
Thermal expansion
Magnetic induction
Mechanical fatigue
Explanation - Corrosion of metals in the body is mainly an electrochemical reaction where metal atoms lose electrons (oxidation) and form ions, which then react with bodily fluids.
Correct answer is: Electrochemical oxidation
Q.2 What is the most common form of corrosion observed on stainless steel implants?
Uniform corrosion
Pitting corrosion
Intergranular corrosion
Stress‑corrosion cracking
Explanation - Pitting corrosion is localized and often occurs on passive alloys like stainless steel when the protective oxide layer is breached, especially in chloride‑rich environments such as body fluids.
Correct answer is: Pitting corrosion
Q.3 Which ion present in body fluids most aggressively attacks titanium alloys?
Sodium (Na⁺)
Chloride (Cl⁻)
Calcium (Ca²⁺)
Potassium (K⁺)
Explanation - Chloride ions can penetrate the passive TiO₂ film on titanium, leading to pitting and crevice corrosion.
Correct answer is: Chloride (Cl⁻)
Q.4 The Nernst equation is used to calculate:
The mechanical strength of a biomaterial
The open‑circuit potential of a corrosion cell
The thermal conductivity of polymers
The dielectric constant of ceramics
Explanation - The Nernst equation relates the electrode potential to ion activities, which is essential for predicting corrosion behavior.
Correct answer is: The open‑circuit potential of a corrosion cell
Q.5 Which surface modification technique is most effective at reducing corrosion of magnesium‑based biodegradable implants?
Anodization
Laser texturing
Plasma immersion ion implantation
Hydroxyapatite coating
Explanation - Hydroxyapatite provides a biocompatible barrier that slows down the rapid degradation of magnesium in physiological conditions.
Correct answer is: Hydroxyapatite coating
Q.6 What does the term "galvanic corrosion" refer to in the context of mixed‑metal implants?
Corrosion due to temperature gradients
Corrosion caused by an electric current from an external source
Accelerated corrosion when two dissimilar metals are electrically coupled
Corrosion induced by mechanical wear
Explanation - When two different metals are in contact in an electrolyte, the more anodic metal corrodes faster, a phenomenon known as galvanic corrosion.
Correct answer is: Accelerated corrosion when two dissimilar metals are electrically coupled
Q.7 Which of the following is NOT a typical degradation product of polymeric biomaterials like PLGA (poly‑lactic‑co‑glycolic acid)?
Lactic acid
Glycolic acid
Carbon dioxide
Hydrochloric acid
Explanation - PLGA hydrolyzes into lactic and glycolic acids, which can further metabolize to CO₂ and water; HCl is not a degradation product.
Correct answer is: Hydrochloric acid
Q.8 In electrochemical impedance spectroscopy (EIS) of a corroding implant, a larger semicircle in the Nyquist plot generally indicates:
Higher corrosion rate
Lower corrosion resistance
Higher charge transfer resistance
Increased surface roughness
Explanation - The diameter of the semicircle corresponds to the charge transfer resistance; a larger diameter means the interface resists corrosion processes more effectively.
Correct answer is: Higher charge transfer resistance
Q.9 Which corrosion mechanism is most closely associated with cyclic mechanical loading of an implant?
Uniform corrosion
Pitting corrosion
Stress‑corrosion cracking (SCC)
Galvanic corrosion
Explanation - SCC occurs when a susceptible material is subjected to tensile stress and a corrosive environment simultaneously, leading to crack initiation and propagation.
Correct answer is: Stress‑corrosion cracking (SCC)
Q.10 The passive film on titanium alloys is primarily composed of:
TiO₂
TiCl₂
TiN
Ti₂O₃
Explanation - A thin, stable TiO₂ layer forms spontaneously on titanium surfaces, providing excellent corrosion resistance in body fluids.
Correct answer is: TiO₂
Q.11 Which factor most significantly accelerates the corrosion of cobalt‑chromium alloys in vivo?
High temperature
Low pH (acidic environment)
High mechanical load
Low oxygen concentration
Explanation - Acidic conditions can destabilize the protective oxide layer on Co‑Cr alloys, increasing corrosion rates.
Correct answer is: Low pH (acidic environment)
Q.12 When measuring corrosion current density (i_corr) using a Tafel extrapolation, a higher i_corr value indicates:
Better biocompatibility
Lower corrosion rate
Higher corrosion rate
Stronger mechanical properties
Explanation - Corrosion current density is directly proportional to the rate at which metal dissolves; a larger i_corr means faster corrosion.
Correct answer is: Higher corrosion rate
Q.13 Which biodegradable metal is most commonly investigated for temporary orthopedic fixation devices?
Stainless steel
Titanium
Magnesium
Gold
Explanation - Magnesium alloys degrade in the body, offering temporary mechanical support while being replaced by natural bone.
Correct answer is: Magnesium
Q.14 The term "crevice corrosion" refers to:
Corrosion at elevated temperatures
Localized attack in confined spaces where the electrolyte is stagnant
Corrosion due to high electrical currents
Uniform loss of metal over the entire surface
Explanation - Crevice corrosion occurs where gaps or shielded areas prevent exchange of ions, leading to aggressive localized degradation.
Correct answer is: Localized attack in confined spaces where the electrolyte is stagnant
Q.15 In the context of corrosion of biomedical implants, the term "biocorrosion" specifically emphasizes:
The role of microbes in accelerating corrosion
The influence of electrical fields
The effect of mechanical wear
The temperature dependence of corrosion
Explanation - Biocorrosion involves microbial activity that can produce corrosive metabolites, increasing degradation rates of implants.
Correct answer is: The role of microbes in accelerating corrosion
Q.16 Which analytical technique provides direct visualization of corrosion pits on an implant surface?
Scanning electron microscopy (SEM)
X‑ray diffraction (XRD)
Fourier‑transform infrared spectroscopy (FTIR)
Differential scanning calorimetry (DSC)
Explanation - SEM offers high‑resolution images that can reveal pit morphology and size on metallic surfaces.
Correct answer is: Scanning electron microscopy (SEM)
Q.17 A biodegradable polymer scaffold shows a mass loss of 20 % after 30 days in simulated body fluid. This loss is primarily due to:
Electrochemical corrosion
Hydrolytic degradation
Oxidative wear
Mechanical fatigue
Explanation - Polymers like PLGA degrade mainly by hydrolysis of ester bonds when immersed in aqueous environments.
Correct answer is: Hydrolytic degradation
Q.18 Which of the following is an advantage of using nitinol (Ni‑Ti alloy) for vascular stents regarding corrosion?
It forms a thick oxide that prevents any ion release
It exhibits shape memory without any corrosion concerns
It develops a stable TiO₂ layer that offers good corrosion resistance
It is completely inert in physiological solutions
Explanation - Nitinol’s surface forms a TiO₂ passive film, granting corrosion resistance similar to pure titanium.
Correct answer is: It develops a stable TiO₂ layer that offers good corrosion resistance
Q.19 Which factor most directly influences the rate of electrochemical corrosion of a metallic biomaterial?
Surface roughness
Electrical conductivity of surrounding tissue
Electrochemical potential difference between metal and electrolyte
Color of the implant
Explanation - Corrosion is driven by the potential difference that creates a driving force for electron flow from the metal to the electrolyte.
Correct answer is: Electrochemical potential difference between metal and electrolyte
Q.20 The primary reason why stainless steel (316L) is still widely used despite the risk of pitting corrosion is:
Its low cost and excellent mechanical strength
Its complete resistance to all forms of corrosion
Its ability to dissolve harmlessly in the body
Its inherent antibacterial properties
Explanation - 316L offers a good balance of mechanical performance and cost, and with proper design and passivation, pitting can be minimized.
Correct answer is: Its low cost and excellent mechanical strength
Q.21 Which of the following electrochemical parameters is most directly related to the thickness of the passive film on a metal?
Open‑circuit potential (OCP)
Charge transfer resistance (R_ct)
Solution resistance (R_s)
Double‑layer capacitance (C_dl)
Explanation - A thicker passive film reduces the double‑layer capacitance because of the increased dielectric distance.
Correct answer is: Double‑layer capacitance (C_dl)
Q.22 A dental implant made of Ti‑6Al‑4V alloy shows increased ion release when exposed to acidic saliva (pH ≈ 4). This is an example of:
Uniform corrosion
Galvanic corrosion
Acid‑induced pitting corrosion
Stress‑corrosion cracking
Explanation - Low pH destabilizes the TiO₂ layer, promoting localized pitting and ion release.
Correct answer is: Acid‑induced pitting corrosion
Q.23 Which corrosion inhibitor is commonly added to the surface of cobalt‑chromium alloy heart valves to improve biocompatibility?
Sodium bicarbonate
Molybdate ions
Chromate conversion coating
Phosphate buffer
Explanation - Chromate conversion layers provide a protective barrier and improve corrosion resistance of Co‑Cr alloys.
Correct answer is: Chromate conversion coating
Q.24 In the degradation of magnesium alloys, the formation of which compound typically leads to hydrogen gas evolution?
Mg(OH)₂
MgCl₂
MgSO₄
MgCO₃
Explanation - Magnesium reacts with water to form magnesium hydroxide and release hydrogen gas, a key concern for in‑situ implants.
Correct answer is: Mg(OH)₂
Q.25 Which of the following best describes the term "corrosion fatigue"?
Corrosion caused by repeated thermal cycles
Fatigue failure that occurs faster due to a corrosive environment
Fatigue that only appears after the metal has fully corroded
Corrosion that happens only under static loading
Explanation - Corrosion fatigue is the synergistic effect of cyclic stress and a corrosive medium accelerating crack initiation and growth.
Correct answer is: Fatigue failure that occurs faster due to a corrosive environment
Q.26 For a polymeric biomaterial, the glass transition temperature (Tg) influences corrosion resistance because:
Below Tg the polymer becomes metallic
Above Tg the polymer swells and allows more water ingress
Tg determines the electrical conductivity
Tg changes the magnetic properties
Explanation - When the polymer is above Tg, chain mobility increases, leading to higher water uptake and accelerated hydrolytic degradation.
Correct answer is: Above Tg the polymer swells and allows more water ingress
Q.27 Which of the following metals is NOT considered bio‑inert for long‑term implantation?
Titanium
Stainless steel 316L
Cobalt‑chromium alloy
Zinc
Explanation - Zinc is biodegradable and releases ions that can be biologically active, thus it is not bio‑inert.
Correct answer is: Zinc
Q.28 The term "passivation" in biomaterials refers to:
Removing surface oxides by acid etching
Forming a thin, protective oxide layer that reduces corrosion
Increasing surface roughness for better cell attachment
Embedding antimicrobial agents into the surface
Explanation - Passivation creates a stable oxide film that acts as a barrier to further metal dissolution.
Correct answer is: Forming a thin, protective oxide layer that reduces corrosion
Q.29 Which corrosion testing method simulates the mechanical loading conditions of a joint replacement while exposing it to a corrosive fluid?
Potentiodynamic polarization
Wear‑corrosion combined testing (tribocorrosion)
Electrochemical impedance spectroscopy
Salt‑spray testing
Explanation - Tribocorrosion combines mechanical wear and electrochemical corrosion, mimicking joint articulation in a fluid environment.
Correct answer is: Wear‑corrosion combined testing (tribocorrosion)
Q.30 Which of the following is a typical sign that a metallic implant is undergoing corrosion in vivo?
Increase in surrounding tissue temperature
Discoloration of the surrounding tissue (e.g., gray‑black staining)
Reduced electrical impedance measured across the implant
Immediate loss of mechanical strength
Explanation - Metal ion release and corrosion products often cause local tissue discoloration (e.g., black staining from titanium particles).
Correct answer is: Discoloration of the surrounding tissue (e.g., gray‑black staining)
Q.31 Which alloying element is added to titanium to improve its corrosion resistance in chloride‑rich environments?
Aluminum
Vanadium
Molybdenum
Gold
Explanation - Molybdenum enhances the stability of the passive TiO₂ layer, especially against pitting in chloride solutions.
Correct answer is: Molybdenum
Q.32 In the context of biodegradable metals, the term "controlled degradation" means:
The metal never degrades at all
The metal degrades at a rate matched to tissue healing
The metal degrades instantaneously after implantation
The metal degrades only when exposed to light
Explanation - Controlled degradation ensures that the implant maintains mechanical support while gradually being replaced by natural tissue.
Correct answer is: The metal degrades at a rate matched to tissue healing
Q.33 Which of the following best describes the effect of fluorides on the corrosion of titanium implants?
Fluorides increase the thickness of the TiO₂ layer
Fluorides have no effect on titanium corrosion
Fluorides can dissolve the TiO₂ passive film, leading to increased corrosion
Fluorides convert titanium into a non‑conductive ceramic
Explanation - Fluoride ions can complex with Ti⁴⁺, destabilizing the protective oxide and promoting pitting corrosion.
Correct answer is: Fluorides can dissolve the TiO₂ passive film, leading to increased corrosion
Q.34 The corrosion rate of a metallic implant can be expressed in mm/year. Which of the following measurements is required to calculate this rate?
Weight loss of the specimen after exposure
Change in color of the surface
Electrical conductivity of the surrounding fluid
Magnetic susceptibility of the implant
Explanation - Weight‑loss measurements, combined with the material density and surface area, allow conversion to a penetration rate (mm/year).
Correct answer is: Weight loss of the specimen after exposure
Q.35 During the electrochemical corrosion of a metal, the region where metal ions are reduced back to metal is called:
Anodic site
Cathodic site
Neutral site
Passivation site
Explanation - Reduction reactions (e.g., O₂ reduction) occur at cathodic sites, while metal oxidation occurs at anodic sites.
Correct answer is: Cathodic site
Q.36 Which of the following surface treatments can convert a titanium surface into a superhydrophilic state, thereby reducing protein adsorption and corrosion?
Anodic oxidation
Laser ablation
Acid etching with hydrofluoric acid
Plasma‑spray coating of hydroxyapatite
Explanation - Anodic oxidation creates a porous TiO₂ layer that is superhydrophilic, discouraging protein adhesion and improving corrosion resistance.
Correct answer is: Anodic oxidation
Q.37 A corrosion test is performed in a solution containing 0.9 % NaCl at 37 °C. This solution is commonly referred to as:
Phosphate‑buffered saline (PBS)
Simulated body fluid (SBF)
Ringer's solution
Normal saline
Explanation - Normal saline (0.9 % NaCl) mimics the ionic strength of extracellular fluid and is frequently used for corrosion testing.
Correct answer is: Normal saline
Q.38 Which parameter is most directly affected by the presence of a protective coating on a metallic implant?
Open‑circuit potential
Elastic modulus
Thermal conductivity
Magnetic permeability
Explanation - A coating changes the surface chemistry, shifting the OCP to more noble (positive) values, indicating better corrosion resistance.
Correct answer is: Open‑circuit potential
Q.39 The corrosion product of iron in a physiological environment often includes:
Fe₂O₃ (hematite)
Fe₃C (cementite)
FeS (iron sulfide)
Fe(OH)₂ (ferrous hydroxide)
Explanation - In aqueous, oxygen‑rich conditions, iron forms ferrous hydroxide as an initial corrosion product.
Correct answer is: Fe(OH)₂ (ferrous hydroxide)
Q.40 Which of the following statements about the 'Stainless Steel 316L' alloy is TRUE regarding its corrosion behavior?
It is completely immune to all forms of corrosion.
It contains a high amount of nickel, which improves corrosion resistance in all environments.
It forms a thin, self‑healing chromium‑oxide layer that provides corrosion resistance.
Its corrosion resistance is solely due to the presence of molybdenum.
Explanation - The Cr₂O₃ passive film on 316L gives it good corrosion resistance, though it can be compromised in aggressive chloride environments.
Correct answer is: It forms a thin, self‑healing chromium‑oxide layer that provides corrosion resistance.
Q.41 In corrosion science, the term "polarization resistance" (Rₚ) is inversely proportional to:
Corrosion current density (i_corr)
Open‑circuit potential (OCP)
Solution resistance (R_s)
Double‑layer capacitance (C_dl)
Explanation - Higher polarization resistance indicates a lower corrosion current density, meaning slower corrosion.
Correct answer is: Corrosion current density (i_corr)
Q.42 Which of the following metals is most likely to cause allergic reactions in patients due to ion release?
Titanium
Zirconium
Nickel
Molybdenum
Explanation - Nickel ions are known allergens; they can be released from alloys containing significant nickel content.
Correct answer is: Nickel
Q.43 When a magnesium alloy implant degrades, the release of Mg²⁺ ions can have which beneficial biological effect?
Stimulate bone formation
Inhibit cell proliferation
Cause severe inflammation
Increase blood clotting
Explanation - Mg²⁺ ions are known to promote osteogenic activity and can aid bone regeneration.
Correct answer is: Stimulate bone formation
Q.44 A biomaterial that degrades via oxidation in the body is most likely:
A polymer containing ester bonds
A metal alloy containing iron
A ceramic composed of hydroxyapatite
A composite of carbon fibers and epoxy
Explanation - Iron corrodes by oxidation, forming iron oxides/hydroxides as degradation products.
Correct answer is: A metal alloy containing iron
Q.45 Which of the following is a major disadvantage of using cobalt‑chromium alloys in orthopedic implants?
Low mechanical strength
High susceptibility to uniform corrosion
Potential release of toxic Co²⁺ ions
Inability to be sterilized
Explanation - Cobalt ions can be cytotoxic and cause adverse tissue reactions if released in significant amounts.
Correct answer is: Potential release of toxic Co²⁺ ions
Q.46 The primary purpose of adding aluminum to titanium alloys (e.g., Ti‑6Al‑4V) is to:
Improve corrosion resistance
Increase density
Enhance mechanical strength and reduce cost
Make the alloy magnetic
Explanation - Aluminum provides solid‑solution strengthening and reduces the overall cost of the alloy.
Correct answer is: Enhance mechanical strength and reduce cost
Q.47 Which method is most suitable for measuring the release rate of metal ions from an implanted device over time?
Inductively coupled plasma mass spectrometry (ICP‑MS)
X‑ray diffraction (XRD)
Thermogravimetric analysis (TGA)
Ultraviolet‑visible spectroscopy (UV‑Vis)
Explanation - ICP‑MS can detect trace metal ion concentrations in biological fluids with high sensitivity.
Correct answer is: Inductively coupled plasma mass spectrometry (ICP‑MS)
Q.48 In a corrosion cell, the region where oxidation of the metal occurs is known as the:
Anode
Cathode
Electrolyte
Reference electrode
Explanation - Oxidation (metal loss) takes place at the anodic site of a corrosion cell.
Correct answer is: Anode
Q.49 Which of the following conditions most strongly promotes crevice corrosion of a stainless steel implant?
High shear stress
Low oxygen concentration within the crevice
Elevated temperature above 100 °C
Presence of ultraviolet light
Explanation - Oxygen depletion inside a crevice leads to a drop in pH and aggressive localized corrosion.
Correct answer is: Low oxygen concentration within the crevice
Q.50 A polymeric scaffold used for tissue engineering is often sterilized by gamma irradiation. How can this sterilization method affect corrosion behavior when the scaffold is later combined with a metallic component?
It makes the polymer conductive, increasing galvanic corrosion.
It introduces free radicals that can accelerate metal oxidation at the interface.
It deposits a protective metal layer on the polymer surface.
It has no effect on corrosion.
Explanation - Gamma irradiation can create reactive species that may enhance corrosion of adjacent metals.
Correct answer is: It introduces free radicals that can accelerate metal oxidation at the interface.
Q.51 The presence of which protein in bodily fluids can accelerate corrosion of metallic implants by forming a conductive biofilm?
Albumin
Fibrinogen
Hemoglobin
Collagen
Explanation - Fibrinogen can adsorb onto metal surfaces, creating a biofilm that facilitates electron transfer and corrosion.
Correct answer is: Fibrinogen
Q.52 Which electrochemical technique is most appropriate for determining the pitting potential (Eₚ) of a metal in simulated body fluid?
Linear sweep voltammetry
Potentiodynamic polarization
Electrochemical impedance spectroscopy
Cyclic voltammetry
Explanation - Potentiodynamic scans reveal the potential at which pitting initiates (Eₚ) as a sudden increase in current.
Correct answer is: Potentiodynamic polarization
Q.53 Which of the following best explains why biodegradable polymers generally have lower corrosion (degradation) rates than magnesium alloys?
Polymers are inert and do not react with water.
Polymers degrade by surface hydrolysis, which is slower than metal dissolution.
Polymers release protective ions that inhibit corrosion.
Polymers have higher electrical conductivity.
Explanation - Hydrolytic cleavage of polymer chains occurs slowly compared with the rapid electrochemical dissolution of metals.
Correct answer is: Polymers degrade by surface hydrolysis, which is slower than metal dissolution.
Q.54 Which of the following is a typical indicator that stress‑corrosion cracking (SCC) is occurring in an implanted device?
Uniform surface pitting
Formation of intergranular cracks aligned with the stress direction
Rapid temperature rise of surrounding tissue
Sudden loss of electrical conductivity
Explanation - SCC produces cracks that follow the tensile stress axis and often propagate along grain boundaries.
Correct answer is: Formation of intergranular cracks aligned with the stress direction
Q.55 For a metallic implant, the term "biocompatibility" primarily refers to:
The ability to resist all forms of corrosion
The ability to integrate with surrounding tissue without adverse reactions
The ability to conduct electricity efficiently
The ability to be easily manufactured
Explanation - Biocompatibility is about the biological response; corrosion resistance contributes but is not the sole factor.
Correct answer is: The ability to integrate with surrounding tissue without adverse reactions
Q.56 A Ti‑6Al‑4V alloy implant is stored in a dry environment for a long period before implantation. Which surface condition is most likely to develop and affect its corrosion behavior once implanted?
Formation of a thick TiO₂ layer
Accumulation of carbonate deposits
Development of a passive aluminum oxide layer
Surface contamination with organic oils
Explanation - Handling and storage can leave oil residues that hinder formation of the protective TiO₂ film, potentially increasing corrosion after implantation.
Correct answer is: Surface contamination with organic oils
Q.57 Which of the following statements is true regarding the use of silver (Ag) nanoparticles in polymeric biomaterials for corrosion protection?
Silver nanoparticles form a continuous metallic coating that blocks corrosion.
Silver ions released can act as antimicrobial agents but may accelerate polymer degradation.
Silver nanoparticles have no effect on corrosion or antimicrobial activity.
Silver makes the polymer magnetic, improving corrosion resistance.
Explanation - Ag⁺ ions provide antimicrobial properties, but their oxidative activity can also promote polymer chain scission.
Correct answer is: Silver ions released can act as antimicrobial agents but may accelerate polymer degradation.
Q.58 When a metallic implant experiences galvanic corrosion, the more noble metal:
Acts as the anode and corrodes faster
Acts as the cathode and corrodes slower
Does not participate in the corrosion process
Is dissolved completely
Explanation - In a galvanic pair, the more noble (cathodic) metal is protected while the less noble (anodic) metal corrodes.
Correct answer is: Acts as the cathode and corrodes slower
Q.59 A biodegradable polymer exhibits a rapid weight loss in the first week of implantation, followed by a slower degradation rate. This behavior is typical of:
Bulk erosion
Surface erosion
Electrochemical corrosion
Stress‑corrosion cracking
Explanation - Surface‑eroding polymers degrade from the exterior, showing an initial fast loss that tapers as the surface area reduces.
Correct answer is: Surface erosion
Q.60 Which of the following alloys is considered the most corrosion‑resistant for long‑term cardiovascular stents?
316L stainless steel
Co‑Cr alloy
Nitinol (Ni‑Ti)
Pure magnesium
Explanation - Nitinol’s stable TiO₂ passive layer provides excellent resistance in the chloride‑rich blood environment.
Correct answer is: Nitinol (Ni‑Ti)
Q.61 Which type of corrosion is most likely when a metal implant is exposed to fluctuating mechanical loads in a corrosive environment?
Uniform corrosion
Pitting corrosion
Stress‑corrosion cracking
Galvanic corrosion
Explanation - Cyclic loading combined with a corrosive medium accelerates crack initiation and growth characteristic of SCC.
Correct answer is: Stress‑corrosion cracking
Q.62 The presence of which ion in the physiological environment can act as a corrosion inhibitor for zinc‑based biodegradable implants?
Phosphate (PO₄³⁻)
Chloride (Cl⁻)
Sulfate (SO₄²⁻)
Fluoride (F⁻)
Explanation - Phosphate can form protective zinc phosphate layers that slow down degradation.
Correct answer is: Phosphate (PO₄³⁻)
Q.63 A corrosion scientist uses a three‑electrode cell for testing. Which electrode acts as the reference electrode?
Working electrode
Counter electrode
Reference electrode
Auxiliary electrode
Explanation - The reference electrode provides a stable, known potential against which the working electrode is measured.
Correct answer is: Reference electrode
Q.64 Which phenomenon explains the increased corrosion rate of a metal when the pH of the surrounding fluid drops from 7.4 to 5.0?
Passivation
Depassivation
Electroplating
Thermal expansion
Explanation - Acidic conditions can dissolve the protective oxide layer, exposing fresh metal to corrosion.
Correct answer is: Depassivation
Q.65 In the context of biomaterial degradation, the term "bioactivity" most often refers to:
The ability of a material to generate an electrical signal
The ability of a material to bond to bone or tissue
The rate at which a material corrodes
The magnetic properties of the material
Explanation - Bioactive materials like hydroxyapatite can form a direct bond with bone, enhancing integration.
Correct answer is: The ability of a material to bond to bone or tissue
Q.66 Which of the following is NOT a typical method for improving the corrosion resistance of a metallic implant?
Anodic oxidation
Applying polymeric coating
Heat treating in a reducing atmosphere
Increasing surface roughness
Explanation - Higher surface roughness generally increases the area exposed to the electrolyte, potentially accelerating corrosion.
Correct answer is: Increasing surface roughness
Q.67 A metallic implant shows a sudden rise in corrosion current after 1000 h of immersion in simulated body fluid. This phenomenon is most likely due to:
Passivation breakdown
Thermal runaway
Magnetic saturation
Mechanical fatigue
Explanation - If the protective oxide film deteriorates over time, corrosion current increases sharply.
Correct answer is: Passivation breakdown
Q.68 Which of the following corrosion mechanisms is most strongly influenced by chloride ions?
Uniform corrosion
Pitting corrosion
Intergranular corrosion
Oxidation corrosion
Explanation - Chloride ions are aggressive in penetrating passive films and initiating pits.
Correct answer is: Pitting corrosion
Q.69 The term "electrochemical potential" in corrosion science is synonymous with:
Voltage measured between two electrodes
Current density
Resistance of the electrolyte
Conductivity of the metal
Explanation - Electrochemical potential refers to the voltage difference that drives electron flow in a corrosion cell.
Correct answer is: Voltage measured between two electrodes
Q.70 Which of the following alloys is a typical choice for dental crowns because of its good corrosion resistance and aesthetic appearance?
Ni‑Cr alloy
Co‑Cr alloy
Gold‑Palladium alloy
Pure iron
Explanation - Gold‑palladium alloys resist corrosion and provide a tooth‑like color.
Correct answer is: Gold‑Palladium alloy
Q.71 A researcher observes that the corrosion rate of a titanium sample increases after it is subjected to a high‑energy laser surface treatment. The most plausible explanation is:
The laser created a thicker TiO₂ layer.
The laser induced micro‑cracks that act as corrosion initiation sites.
The laser removed all surface oxides, making the surface inert.
The laser changed the crystal structure to a more noble phase.
Explanation - Laser ablation can produce micro‑defects that compromise the protective oxide film, increasing corrosion susceptibility.
Correct answer is: The laser induced micro‑cracks that act as corrosion initiation sites.
Q.72 Which of the following is the most common method for evaluating the mechanical integrity of a corroded metallic implant?
Scanning electron microscopy (SEM)
Tensile testing
Potentiodynamic polarization
Fourier‑transform infrared spectroscopy (FTIR)
Explanation - Tensile tests assess whether corrosion has reduced the load‑bearing capacity of the implant.
Correct answer is: Tensile testing
Q.73 The 'breakdown potential' measured during a polarization test indicates:
The voltage at which the metal starts to dissolve uniformly.
The voltage at which the protective passive film fails and pitting begins.
The voltage at which the electrolyte becomes conductive.
The voltage at which the metal becomes magnetic.
Explanation - Breakdown potential (E_break) marks the onset of localized pitting corrosion.
Correct answer is: The voltage at which the protective passive film fails and pitting begins.
Q.74 In biodegradable magnesium implants, which alloying element is commonly added to improve corrosion resistance without sacrificing biodegradability?
Aluminum
Zinc
Copper
Lead
Explanation - Zn improves mechanical strength and slows degradation while remaining biocompatible.
Correct answer is: Zinc
Q.75 Which type of corrosion is characterized by the simultaneous action of mechanical wear and electrochemical attack?
Uniform corrosion
Pitting corrosion
Tribocorrosion
Intergranular corrosion
Explanation - Tribocorrosion combines mechanical abrasion with electrochemical processes, typical for joint implants.
Correct answer is: Tribocorrosion
Q.76 When a metallic implant is placed in a phosphate‑buffered saline (PBS) solution, the presence of phosphate ions primarily helps to:
Increase the corrosion rate
Form protective phosphate layers on the metal surface
Make the solution more acidic
Promote bacterial growth
Explanation - Phosphate ions can precipitate as metal phosphates, providing an additional protective barrier.
Correct answer is: Form protective phosphate layers on the metal surface
Q.77 Which of the following statements is true regarding the degradation of bioactive glasses used as bone grafts?
They dissolve rapidly, releasing toxic silica particles.
They form a hydroxycarbonate apatite layer that bonds to bone and gradually dissolve.
They are completely inert and never degrade.
Their degradation is purely mechanical, not chemical.
Explanation - Bioactive glasses develop an HCA layer that supports bone bonding and slowly resorbs over time.
Correct answer is: They form a hydroxycarbonate apatite layer that bonds to bone and gradually dissolve.
Q.78 What is the main advantage of using a ceramic coating (e.g., Al₂O₃) on a metallic implant?
Improves electrical conductivity
Reduces friction and provides a barrier to corrosion
Makes the implant magnetic
Increases the implant’s density
Explanation - Ceramic coatings are hard, chemically inert, and protect the underlying metal from corrosive attack.
Correct answer is: Reduces friction and provides a barrier to corrosion
Q.79 The term "electrochemical series" is important for predicting galvanic corrosion because it ranks metals according to:
Mechanical hardness
Standard electrode potentials
Thermal conductivity
Density
Explanation - Metals higher in the series are more noble and act as cathodes when coupled with less noble metals.
Correct answer is: Standard electrode potentials
Q.80 A biodegradable polymer scaffold shows a sudden increase in degradation rate after 4 weeks in vivo. This change is most likely caused by:
Enzymatic degradation becoming dominant
Loss of mechanical stress
Temperature increase
Magnetic field exposure
Explanation - After initial hydrolysis, enzymes can accelerate polymer chain cleavage, raising the degradation rate.
Correct answer is: Enzymatic degradation becoming dominant
Q.81 Which of the following is the primary driver for corrosion of a metal in a physiological environment?
Electrical conductivity of the metal
Presence of an electrochemical potential difference
Magnetic field strength
Mechanical stiffness
Explanation - Corrosion proceeds when there is a potential difference that allows electrons to flow from metal to the electrolyte.
Correct answer is: Presence of an electrochemical potential difference
Q.82 A research article reports that adding 0.5 wt% of rare‑earth element yttrium to a magnesium alloy reduces its corrosion rate by 30 % in simulated body fluid. This improvement is mainly due to:
Yttrium forming a more protective oxide layer
Yttrium increasing the alloy’s electrical resistance
Yttrium decreasing the alloy’s density
Yttrium making the alloy magnetic
Explanation - Rare‑earth elements can refine grain structure and promote formation of stable, protective oxides.
Correct answer is: Yttrium forming a more protective oxide layer
Q.83 Which testing condition most closely mimics the dynamic flow of blood over a coronary stent during corrosion testing?
Static immersion in saline
Rotating‑disk electrode setup
Pulsatile flow loop with simulated blood
Drop‑tower impact test
Explanation - A flow loop reproduces shear stresses and mass transport conditions similar to those in vivo.
Correct answer is: Pulsatile flow loop with simulated blood
Q.84 Which of the following statements about the degradation of biodegradable zinc alloys is correct?
Zinc degrades faster than magnesium in physiological conditions.
Zinc degrades primarily through oxidation, releasing Zn²⁺ ions that can be beneficial for bone growth.
Zinc is completely inert in the body and does not degrade.
Zinc degrades only under high‑temperature conditions.
Explanation - Zinc corrodes to Zn²⁺, which can stimulate osteogenesis, and its degradation rate is moderate, slower than Mg but faster than some steels.
Correct answer is: Zinc degrades primarily through oxidation, releasing Zn²⁺ ions that can be beneficial for bone growth.
Q.85 What is the main purpose of applying a cathodic protection system to a metallic implant?
To increase the implant’s electrical conductivity
To make the implant magnetic
To shift the metal’s potential more negative, preventing anodic dissolution
To heat the implant and sterilize it
Explanation - Cathodic protection supplies electrons to the metal, making it the cathode and suppressing corrosion.
Correct answer is: To shift the metal’s potential more negative, preventing anodic dissolution
Q.86 Which of the following metals is most susceptible to stress‑corrosion cracking in the presence of chloride ions?
Titanium
Stainless steel 316L
Gold
Platinum
Explanation - 316L can suffer SCC in chloride‑rich environments, especially under tensile stress.
Correct answer is: Stainless steel 316L
Q.87 During a corrosion study, the measured corrosion potential (E_corr) of a titanium sample is -0.2 V vs. SHE. A more noble (positive) E_corr value would indicate:
Higher corrosion rate
Lower corrosion rate
Higher mechanical strength
Higher electrical conductivity
Explanation - A more positive corrosion potential generally means the metal is less prone to oxidation, indicating better corrosion resistance.
Correct answer is: Lower corrosion rate
Q.88 Which of the following is a common symptom of metal ion release from a failing implant?
Hair loss
Localized inflammation and pain
Improved bone density
Decreased blood pressure
Explanation - Metal ions can trigger an immune response, leading to inflammation and discomfort around the implant site.
Correct answer is: Localized inflammation and pain
Q.89 The addition of which element to a magnesium alloy most effectively reduces its corrosion rate without severely compromising its mechanical properties?
Aluminum
Zinc
Copper
Lead
Explanation - Zinc improves corrosion resistance and maintains good mechanical strength in Mg alloys.
Correct answer is: Zinc
Q.90 Which of the following best describes the phenomenon of 'hydrogen embrittlement' in metallic implants?
Hydrogen atoms dissolve the metal surface, making it smoother.
Hydrogen diffuses into the metal lattice, reducing ductility and causing cracking.
Hydrogen forms a protective layer that stops corrosion.
Hydrogen increases the electrical conductivity of the metal.
Explanation - Hydrogen generated during corrosion can enter the metal, leading to loss of toughness and brittle fracture.
Correct answer is: Hydrogen diffuses into the metal lattice, reducing ductility and causing cracking.
Q.91 A polymeric biomaterial that degrades primarily by surface erosion is likely to exhibit which of the following mass‑loss profiles?
Linear mass loss over time
Exponential increase in mass loss after an initial lag
Constant mass loss rate regardless of surface area
Zero mass loss until complete failure
Explanation - Surface erosion removes material layer by layer, leading to a relatively constant rate of mass loss.
Correct answer is: Linear mass loss over time
Q.92 Which testing method provides real‑time monitoring of corrosion product formation on an implant surface?
Electrochemical impedance spectroscopy (EIS)
Scanning electron microscopy (SEM)
X‑ray diffraction (XRD)
Differential scanning calorimetry (DSC)
Explanation - EIS can detect changes in surface impedance associated with the growth of corrosion layers.
Correct answer is: Electrochemical impedance spectroscopy (EIS)
Q.93 Which of the following is an advantage of using a biodegradable polymer over a metallic implant for temporary tissue scaffolding?
Higher load‑bearing capacity
No need for a second surgery to remove the implant
Zero risk of any corrosion
Complete electrical conductivity
Explanation - Biodegradable polymers naturally resorb, eliminating the need for removal after healing.
Correct answer is: No need for a second surgery to remove the implant
Q.94 In a corrosion cell, the solution resistance (R_s) primarily depends on:
The thickness of the metal foil
The conductivity and geometry of the electrolyte
The magnetic field surrounding the cell
The temperature of the metal
Explanation - R_s is governed by how easily ions can move through the electrolyte and the distance between electrodes.
Correct answer is: The conductivity and geometry of the electrolyte
Q.95 Which alloy is commonly used for vascular stents due to its combination of shape memory and corrosion resistance?
Stainless steel 304
Nitinol (Ni‑Ti)
Copper‑zinc alloy
Pure aluminum
Explanation - Nitinol’s superelasticity and stable TiO₂ passive film make it suitable for stent applications.
Correct answer is: Nitinol (Ni‑Ti)
Q.96 A corrosion scientist observes that after 48 h of immersion, a cobalt‑chromium sample exhibits a current density of 2 µA/cm². If the current density doubles after another 48 h, what can be inferred?
The corrosion rate is decreasing.
The protective film is deteriorating, leading to faster corrosion.
The sample has become completely inert.
The solution has become less conductive.
Explanation - Increasing current density indicates a higher rate of metal dissolution, often due to film breakdown.
Correct answer is: The protective film is deteriorating, leading to faster corrosion.
Q.97 Which of the following is the most appropriate method to assess the in‑vitro degradation rate of a biodegradable polymer scaffold?
Measuring pH changes in the immersion medium
Recording changes in electrical resistance
Quantifying mass loss over predetermined intervals
Observing color change of the scaffold
Explanation - Mass loss directly reflects the amount of material degraded, providing a clear degradation rate.
Correct answer is: Quantifying mass loss over predetermined intervals
Q.98 Which of the following statements best describes the role of an oxide film on titanium implants?
It makes the implant magnetic.
It acts as a barrier that significantly reduces corrosion.
It increases the electrical conductivity of the implant.
It dissolves immediately upon implantation.
Explanation - The TiO₂ passive film protects the underlying metal from aggressive ions in bodily fluids.
Correct answer is: It acts as a barrier that significantly reduces corrosion.
Q.99 When a metallic biomaterial is subjected to cyclic loading in a corrosive environment, which degradation mechanism is most likely to dominate?
Uniform corrosion
Stress‑corrosion cracking
Electroplating
Thermal oxidation
Explanation - Cyclic tensile stresses combined with a corrosive medium accelerate SCC.
Correct answer is: Stress‑corrosion cracking
Q.100 Which of the following is a common indicator that a metal alloy is undergoing galvanic corrosion in the body?
Uniform surface darkening
Localized pits adjacent to a different metal
Increase in overall body temperature
Decrease in blood pH
Explanation - Galvanic coupling leads to localized corrosion at the anodic metal near the cathodic partner.
Correct answer is: Localized pits adjacent to a different metal
Q.101 A researcher wants to simulate the degradation of a biodegradable magnesium implant over 12 months. Which accelerated testing method is most appropriate?
Increasing the temperature of the immersion solution
Reducing the pH of the solution to 3.0
Adding a high concentration of chloride ions
All of the above
Explanation - Higher temperature, lower pH, and increased chloride accelerate magnesium corrosion, providing a faster assessment of long‑term behavior.
Correct answer is: All of the above
Q.102 Which of the following corrosion inhibitors is commonly used to improve the corrosion resistance of stainless steel in biomedical devices?
Sodium nitrate
Molybdate (MoO₄²⁻)
Copper sulfate
Lead acetate
Explanation - Molybdate ions help form protective films on stainless steel, reducing pitting susceptibility.
Correct answer is: Molybdate (MoO₄²⁻)
Q.103 Which of the following statements about the corrosion of pure iron implants is correct?
Iron is completely inert in the body.
Iron corrodes rapidly, producing toxic Fe³⁺ ions.
Iron corrodes slowly, and its degradation products can be metabolized.
Iron forms a permanent protective coating that never degrades.
Explanation - Iron undergoes slow corrosion, and the resulting iron ions can be incorporated into the body’s iron metabolism.
Correct answer is: Iron corrodes slowly, and its degradation products can be metabolized.
Q.104 A biomaterial scientist wishes to compare the corrosion resistance of two alloys. Which parameter from potentiodynamic polarization curves is most appropriate for this comparison?
Corrosion potential (E_corr)
Tafel slope
Current density at breakdown potential
Corrosion current density (i_corr)
Explanation - i_corr directly reflects the rate at which metal dissolves; lower i_corr means better resistance.
Correct answer is: Corrosion current density (i_corr)
Q.105 During the degradation of a biodegradable polymer, the appearance of a sharp decrease in pH of the surrounding solution is most likely caused by:
Release of basic ions
Generation of acidic degradation products such as lactic acid
Absorption of atmospheric CO₂
Electrochemical oxidation of the polymer
Explanation - Hydrolysis of ester bonds in polymers like PLGA releases lactic and glycolic acids, lowering pH.
Correct answer is: Generation of acidic degradation products such as lactic acid
Q.106 Which of the following metals is most commonly used for permanent dental implants due to its excellent corrosion resistance and biocompatibility?
Titanium
Copper
Aluminum
Zinc
Explanation - Titanium forms a stable TiO₂ layer, offering high corrosion resistance and compatibility with bone tissue.
Correct answer is: Titanium
Q.107 The phenomenon where a metal corrodes faster at the crack tip under tensile stress is known as:
Pitting corrosion
Uniform corrosion
Stress‑corrosion cracking
Electroplating
Explanation - SCC accelerates corrosion at stressed regions, especially at crack tips.
Correct answer is: Stress‑corrosion cracking
Q.108 A polymeric bone scaffold is coated with a thin layer of calcium phosphate. The primary purpose of this coating is to:
Increase the scaffold’s electrical conductivity
Improve osteointegration and reduce degradation rate
Make the scaffold magnetic
Prevent any water absorption
Explanation - Calcium phosphate promotes bone bonding and can act as a barrier to water, slowing polymer hydrolysis.
Correct answer is: Improve osteointegration and reduce degradation rate
Q.109 Which of the following best explains why a higher chloride concentration in simulated body fluid leads to an increased pitting corrosion rate of stainless steel?
Chloride ions increase the solution’s viscosity.
Chloride ions destabilize the protective chromium‑oxide layer.
Chloride ions raise the temperature of the solution.
Chloride ions form a protective layer on the metal.
Explanation - Chloride ions penetrate and break down the Cr₂O₃ film, allowing localized pits to form.
Correct answer is: Chloride ions destabilize the protective chromium‑oxide layer.
Q.110 When a metallic implant is exposed to an oxidative environment, the primary electrochemical reaction at the anode is:
Reduction of oxygen
Oxidation of metal to metal ions
Formation of hydrogen gas
Deposition of metal
Explanation - At the anode, metal atoms lose electrons, forming cations that enter the solution.
Correct answer is: Oxidation of metal to metal ions
Q.111 Which of the following is a major concern when using magnesium alloys for orthopedic implants?
Excessive mechanical strength
Rapid hydrogen gas evolution causing gas pockets
Magnetic interference with MRI
High cost compared to titanium
Explanation - Mg corrosion produces hydrogen, which can accumulate as gas bubbles in tissue.
Correct answer is: Rapid hydrogen gas evolution causing gas pockets
Q.112 In electrochemical corrosion testing, the reference electrode commonly used for physiological studies is:
Saturated calomel electrode (SCE)
Silver/silver chloride (Ag/AgCl) electrode
Copper/copper sulfate electrode
Platinum electrode
Explanation - Ag/AgCl provides a stable reference potential in chloride‑containing solutions like simulated body fluid.
Correct answer is: Silver/silver chloride (Ag/AgCl) electrode
Q.113 A biodegradable polymer experiences a sudden increase in degradation rate after 8 weeks in vivo. This is most likely due to:
Mechanical failure of the polymer matrix
Enzyme‑mediated hydrolysis becoming dominant
Temperature rise in the tissue
External electromagnetic field exposure
Explanation - After initial hydrolysis, enzymes in the body can accelerate polymer breakdown.
Correct answer is: Enzyme‑mediated hydrolysis becoming dominant
Q.114 Which of the following metals is typically avoided for long‑term implants due to its high susceptibility to corrosion and ion release?
Titanium
Cobalt‑chromium alloy
Stainless steel 316L
Nickel
Explanation - Nickel can cause allergic reactions and corrodes relatively easily compared to Ti or Co‑Cr.
Correct answer is: Nickel
Q.115 A corrosion scientist notes that after surface polishing, a titanium alloy shows a higher corrosion current density than before polishing. The likely cause is:
Polishing removed the protective oxide layer, exposing fresh metal.
Polishing introduced micro‑cracks that accelerate corrosion.
Polishing increased the alloy’s electrical conductivity.
Polishing added a protective polymer film.
Explanation - Mechanical polishing can strip the passive TiO₂ layer, leading to higher corrosion rates until it reforms.
Correct answer is: Polishing removed the protective oxide layer, exposing fresh metal.
Q.116 Which of the following is an advantage of using hydroxyapatite coatings on metallic implants?
They make the implant magnetic.
They improve corrosion resistance and promote bone bonding.
They increase the implant’s electrical conductivity.
They prevent any mechanical loading on the implant.
Explanation - Hydroxyapatite forms a biocompatible barrier that reduces ion release and encourages osseointegration.
Correct answer is: They improve corrosion resistance and promote bone bonding.
Q.117 Which factor primarily determines the rate of electrochemical corrosion of a metal in a physiological environment?
The metal’s magnetic permeability
The electrochemical potential difference between the metal and the surrounding fluid
The metal’s density
The color of the metal surface
Explanation - A larger potential difference drives electron flow and accelerates corrosion.
Correct answer is: The electrochemical potential difference between the metal and the surrounding fluid
Q.118 What is the primary role of magnesium ions (Mg²⁺) released from degrading Mg‑based implants?
They cause severe toxicity in surrounding tissue.
They act as a co‑factor for many cellular processes and can aid bone healing.
They increase the electrical conductivity of the tissue.
They form a permanent protective layer on the implant.
Explanation - Mg²⁺ is an essential ion that can stimulate bone cell activity and is generally well‑tolerated at controlled levels.
Correct answer is: They act as a co‑factor for many cellular processes and can aid bone healing.
Q.119 When a metal implant is placed in a phosphate‑buffered saline (PBS) solution at 37 °C, the primary purpose of the phosphate ions is to:
Increase the pH to alkaline levels
Form protective phosphate films on the metal surface
Accelerate the corrosion process
Act as a catalyst for hydrogen evolution
Explanation - Phosphate ions can precipitate as metal phosphates, providing an additional protective layer.
Correct answer is: Form protective phosphate films on the metal surface