Q.1 Which of the following elements is a lanthanide?
Cerium (Ce)
Uranium (U)
Thorium (Th)
Plutonium (Pu)
Explanation - Lanthanides are the 14 elements from La (57) to Lu (71). Cerium falls within this series.
Correct answer is: Cerium (Ce)
Q.2 Which actinide is commonly used as fuel in nuclear reactors?
Thorium (Th)
Uranium (U)
Neptunium (Np)
Plutonium (Pu)
Explanation - Uranium-235 and Uranium-238 are commonly used as fuel in nuclear reactors due to their fissionable properties.
Correct answer is: Uranium (U)
Q.3 The common oxidation state of most lanthanides is:
+2
+3
+4
+5
Explanation - Lanthanides mostly exhibit +3 oxidation state because of the stability of the f-orbitals.
Correct answer is: +3
Q.4 Which of the following is an actinide?
Neodymium (Nd)
Plutonium (Pu)
Samarium (Sm)
Gadolinium (Gd)
Explanation - Actinides include elements from actinium (89) to lawrencium (103). Plutonium is an actinide.
Correct answer is: Plutonium (Pu)
Q.5 The term 'lanthanide contraction' refers to:
Gradual decrease in atomic radii of lanthanides
Increase in melting points of lanthanides
Radioactivity of lanthanides
Formation of complex ions
Explanation - Due to poor shielding of 4f electrons, atomic radii of lanthanides decrease gradually, known as lanthanide contraction.
Correct answer is: Gradual decrease in atomic radii of lanthanides
Q.6 Which lanthanide is most abundant in the Earth's crust?
Lanthanum (La)
Cerium (Ce)
Neodymium (Nd)
Samarium (Sm)
Explanation - Cerium is the most abundant lanthanide, comprising about 0.0046% of the Earth's crust.
Correct answer is: Cerium (Ce)
Q.7 Which actinide is used in smoke detectors?
Thorium (Th)
Uranium (U)
Americium (Am)
Plutonium (Pu)
Explanation - Americium-241 emits alpha particles and is used in ionization-type smoke detectors.
Correct answer is: Americium (Am)
Q.8 Which of the following properties is common for both lanthanides and actinides?
High melting points
Formation of coloured ions
Radioactivity
Non-metallic nature
Explanation - Both lanthanides and actinides form coloured ions due to f-f electronic transitions.
Correct answer is: Formation of coloured ions
Q.9 The element with atomic number 90 is:
Thorium (Th)
Protactinium (Pa)
Uranium (U)
Neptunium (Np)
Explanation - Thorium has atomic number 90 and is the first naturally occurring actinide.
Correct answer is: Thorium (Th)
Q.10 Which of the following lanthanides is used in strong permanent magnets?
Gadolinium (Gd)
Neodymium (Nd)
Lanthanum (La)
Europium (Eu)
Explanation - Neodymium is used in Nd-Fe-B magnets due to its high magnetic strength.
Correct answer is: Neodymium (Nd)
Q.11 Which actinide element was first artificially synthesized?
Plutonium (Pu)
Neptunium (Np)
Americium (Am)
Curium (Cm)
Explanation - Neptunium (atomic number 93) was the first actinide to be synthesized artificially in 1940.
Correct answer is: Neptunium (Np)
Q.12 The most stable oxidation state of Uranium in aqueous solution is:
+4
+5
+6
+3
Explanation - Uranium most commonly exists in the +6 oxidation state as the uranyl ion (UO2)2+ in aqueous solution.
Correct answer is: +6
Q.13 Which lanthanide is used in red phosphors for TV screens?
Europium (Eu)
Gadolinium (Gd)
Samarium (Sm)
Terbium (Tb)
Explanation - Europium is used in red phosphors in TV and LED screens due to its luminescent properties.
Correct answer is: Europium (Eu)
Q.14 Which actinide is highly radioactive and used in atomic bombs?
Thorium (Th)
Uranium (U)
Plutonium (Pu)
Neptunium (Np)
Explanation - Plutonium-239 is fissile and was used in nuclear weapons due to its ability to sustain chain reactions.
Correct answer is: Plutonium (Pu)
Q.15 Which property increases across the lanthanide series?
Atomic radius
Electronegativity
Ionization energy
Both b and c
Explanation - Across the lanthanide series, electronegativity and ionization energy increase due to lanthanide contraction.
Correct answer is: Both b and c
Q.16 Which element is called 'cerium rare-earth'?
Cerium (Ce)
Lanthanum (La)
Praseodymium (Pr)
Neodymium (Nd)
Explanation - Cerium is often referred to as a 'rare-earth element' and is the most abundant lanthanide.
Correct answer is: Cerium (Ce)
Q.17 Which of the following is used as a neutron absorber in nuclear reactors?
Gadolinium (Gd)
Uranium (U)
Thorium (Th)
Americium (Am)
Explanation - Gadolinium has a high neutron capture cross-section and is used to control reactivity in reactors.
Correct answer is: Gadolinium (Gd)
Q.18 Actinides are generally:
Non-radioactive metals
Radioactive metals
Non-metals
Metalloids
Explanation - All actinides are radioactive, and many are used in nuclear applications.
Correct answer is: Radioactive metals
Q.19 Which of the following lanthanides is used in camera lenses to reduce chromatic aberration?
Lanthanum (La)
Europium (Eu)
Neodymium (Nd)
Gadolinium (Gd)
Explanation - Lanthanum oxide is used in optical glass for camera lenses due to its high refractive index.
Correct answer is: Lanthanum (La)
Q.20 The actinide contraction is analogous to:
Lanthanide contraction
Transition metal contraction
Alkali metal contraction
Halogen contraction
Explanation - Actinides show a decrease in atomic and ionic radii across the series due to poor shielding of 5f electrons, similar to lanthanides.
Correct answer is: Lanthanide contraction
Q.21 Which of the following lanthanides is commonly used in strong magnets and speakers?
Neodymium (Nd)
Lanthanum (La)
Samarium (Sm)
Gadolinium (Gd)
Explanation - Samarium-cobalt (SmCo) magnets are used in high-temperature and high-strength magnetic applications.
Correct answer is: Samarium (Sm)
Q.22 Which actinide is used in radioisotope thermoelectric generators (RTGs)?
Uranium (U)
Plutonium (Pu)
Thorium (Th)
Americium (Am)
Explanation - Plutonium-238 is used in RTGs for spacecraft due to its heat from radioactive decay.
Correct answer is: Plutonium (Pu)
Q.23 Which of the following lanthanides is used in green phosphors for color TVs?
Terbium (Tb)
Europium (Eu)
Gadolinium (Gd)
Samarium (Sm)
Explanation - Terbium compounds emit green light and are used in TV phosphors.
Correct answer is: Terbium (Tb)
Q.24 Which actinide has the highest atomic number found naturally?
Uranium (U)
Thorium (Th)
Neptunium (Np)
Plutonium (Pu)
Explanation - Uranium (atomic number 92) is the heaviest naturally occurring actinide element.
Correct answer is: Uranium (U)
Q.25 The first ionization energy of actinides generally:
Decreases across the series
Increases across the series
Remains constant
Shows no trend
Explanation - Due to the actinide contraction, ionization energies slightly increase across the series.
Correct answer is: Increases across the series