Q.1 Who proposed the 'Plum Pudding' model of the atom?
Ernest Rutherford
J.J. Thomson
Niels Bohr
James Chadwick
Explanation - J.J. Thomson proposed the 'Plum Pudding' model in 1904, suggesting that atoms consist of electrons embedded in a positively charged sphere.
Correct answer is: J.J. Thomson
Q.2 Which particle determines the chemical behavior of an atom?
Proton
Neutron
Electron
Nucleus
Explanation - Electrons, especially valence electrons, are responsible for chemical reactions and bonding.
Correct answer is: Electron
Q.3 The discovery of the neutron is credited to:
Ernest Rutherford
James Chadwick
Niels Bohr
Albert Einstein
Explanation - James Chadwick discovered the neutron in 1932, completing the basic picture of the atomic nucleus.
Correct answer is: James Chadwick
Q.4 Which quantum number describes the shape of an orbital?
Principal quantum number (n)
Azimuthal quantum number (l)
Magnetic quantum number (m)
Spin quantum number (s)
Explanation - The azimuthal or angular momentum quantum number (l) defines the shape of the orbital (s, p, d, f).
Correct answer is: Azimuthal quantum number (l)
Q.5 What is the maximum number of electrons that can occupy an s orbital?
2
6
10
14
Explanation - An s orbital can hold a maximum of 2 electrons due to the Pauli exclusion principle.
Correct answer is: 2
Q.6 The radius of an atom is largely determined by:
Number of neutrons
Number of protons
Number of electrons and their energy levels
Atomic mass
Explanation - Atomic radius depends on the distance of the outermost electrons from the nucleus.
Correct answer is: Number of electrons and their energy levels
Q.7 Which of the following is NOT a postulate of Bohr’s atomic model?
Electrons revolve in fixed orbits
Electrons emit radiation while revolving
Energy levels are quantized
Electron transitions involve absorption or emission of energy
Explanation - Bohr postulated that electrons do NOT emit radiation while in a stationary orbit; radiation occurs only during transitions.
Correct answer is: Electrons emit radiation while revolving
Q.8 Who performed the gold foil experiment?
J.J. Thomson
Ernest Rutherford
Niels Bohr
Robert Millikan
Explanation - Rutherford’s gold foil experiment in 1911 led to the discovery of the atomic nucleus.
Correct answer is: Ernest Rutherford
Q.9 Which principle states that no two electrons in an atom can have the same set of four quantum numbers?
Heisenberg Uncertainty Principle
Pauli Exclusion Principle
Aufbau Principle
Hund's Rule
Explanation - The Pauli Exclusion Principle restricts two electrons from having identical quantum numbers in the same atom.
Correct answer is: Pauli Exclusion Principle
Q.10 The Aufbau principle helps in determining:
Electron spin
Order of electron filling in orbitals
Energy of photons emitted
Atomic radius
Explanation - Aufbau principle states that electrons fill lower energy orbitals first before occupying higher ones.
Correct answer is: Order of electron filling in orbitals
Q.11 What is the shape of a p-orbital?
Spherical
Dumbbell
Cloverleaf
Double dumbbell
Explanation - p orbitals have a dumbbell shape with two lobes on opposite sides of the nucleus.
Correct answer is: Dumbbell
Q.12 Which of the following represents the isotope of carbon?
12C
12N
12O
12H
Explanation - 12C is an isotope of carbon, having the same number of protons but possibly different neutrons compared to other carbon isotopes.
Correct answer is: 12C
Q.13 The spin quantum number can have values of:
0 and 1
1/2 and -1/2
1 and -1
0 and 1/2
Explanation - Spin quantum number indicates the intrinsic spin of an electron, which can be +1/2 or -1/2.
Correct answer is: 1/2 and -1/2
Q.14 Which of the following has the highest penetrating power?
Alpha particles
Beta particles
Gamma rays
Neutrons
Explanation - Gamma rays have no mass or charge and can penetrate most materials more deeply than alpha or beta particles.
Correct answer is: Gamma rays
Q.15 The concept of orbitals was introduced by:
Bohr
Schrödinger
Heisenberg
Rutherford
Explanation - Schrödinger proposed the quantum mechanical model where electrons exist in orbitals defined by probability distributions.
Correct answer is: Schrödinger
Q.16 Which of the following is true about isotopes?
Same number of neutrons, different protons
Same number of protons, different neutrons
Different number of protons and electrons
Same atomic mass, different protons
Explanation - Isotopes have identical atomic numbers but different mass numbers due to varying neutrons.
Correct answer is: Same number of protons, different neutrons
Q.17 Heisenberg’s uncertainty principle is related to the uncertainty in:
Energy and time
Position and momentum
Charge and mass
Speed and acceleration
Explanation - The principle states it is impossible to simultaneously determine the exact position and momentum of a particle.
Correct answer is: Position and momentum
Q.18 Which of the following determines the energy of an electron in an atom?
Principal quantum number (n)
Spin quantum number (s)
Magnetic quantum number (m)
Azimuthal quantum number (l)
Explanation - The principal quantum number (n) defines the energy level of an electron in an atom.
Correct answer is: Principal quantum number (n)
Q.19 The unit of atomic mass is:
kg
g
amu
mol
Explanation - Atomic mass is measured in atomic mass units (amu), where 1 amu = 1/12th the mass of a carbon-12 atom.
Correct answer is: amu
Q.20 Hund's rule states that:
Electrons fill lower orbitals first
No two electrons can have same quantum numbers
Every orbital in a subshell is singly occupied before pairing
Electrons occupy the nucleus first
Explanation - Hund’s rule maximizes the number of unpaired electrons with parallel spins in degenerate orbitals.
Correct answer is: Every orbital in a subshell is singly occupied before pairing
Q.21 Which of the following radiation is deflected by magnetic and electric fields?
Alpha particles
Beta particles
Gamma rays
Both alpha and beta particles
Explanation - Charged particles like alpha (+) and beta (-) are deflected by magnetic and electric fields, whereas gamma rays are neutral.
Correct answer is: Both alpha and beta particles
Q.22 The mass number of an atom is:
Number of protons
Number of neutrons
Sum of protons and neutrons
Number of electrons
Explanation - Mass number (A) = Number of protons + Number of neutrons in the nucleus.
Correct answer is: Sum of protons and neutrons
Q.23 Which model first introduced the concept of discrete energy levels?
Rutherford model
Thomson model
Bohr model
Schrödinger model
Explanation - Bohr introduced discrete or quantized energy levels for electrons in hydrogen-like atoms.
Correct answer is: Bohr model
Q.24 Which of the following particles has negligible mass?
Proton
Neutron
Electron
Alpha particle
Explanation - Electrons have negligible mass compared to protons and neutrons.
Correct answer is: Electron
Q.25 Which phenomenon confirmed the wave nature of electrons?
Photoelectric effect
Double-slit experiment
Compton scattering
Rutherford scattering
Explanation - Electron diffraction in the double-slit experiment demonstrated the wave nature of electrons.
Correct answer is: Double-slit experiment