Q.1 Who proposed the nuclear model of the atom?
J.J. Thomson
Ernest Rutherford
Niels Bohr
James Chadwick
Explanation - Rutherford proposed the nuclear model of the atom in which electrons revolve around a dense nucleus.
Correct answer is: Ernest Rutherford
Q.2 Which particle was discovered by James Chadwick?
Proton
Electron
Neutron
Photon
Explanation - James Chadwick discovered the neutron in 1932, which explained the missing mass of nuclei.
Correct answer is: Neutron
Q.3 The mass number of an atom represents:
Number of protons
Number of neutrons
Sum of protons and neutrons
Number of electrons
Explanation - Mass number (A) = Protons (Z) + Neutrons (N).
Correct answer is: Sum of protons and neutrons
Q.4 The atomic number of an element is equal to:
Number of neutrons
Number of protons
Mass number
Protons + neutrons
Explanation - The atomic number (Z) is defined as the number of protons in the nucleus of an atom.
Correct answer is: Number of protons
Q.5 Which force binds protons and neutrons inside the nucleus?
Electromagnetic force
Gravitational force
Nuclear force
Weak force
Explanation - The strong nuclear force binds protons and neutrons inside the atomic nucleus despite the repulsion between protons.
Correct answer is: Nuclear force
Q.6 In Bohr’s model of hydrogen, the angular momentum of electron is quantized as:
nh
nh/π
nh/2π
n²h/2π
Explanation - Bohr postulated that the angular momentum of electron in orbit is quantized as L = n(h/2π).
Correct answer is: nh/2π
Q.7 The energy of the electron in the nth orbit of hydrogen is proportional to:
1/n²
n²
1/n
n
Explanation - In Bohr’s model, energy of electron in nth orbit is E ∝ -1/n².
Correct answer is: 1/n²
Q.8 Which transition in hydrogen gives rise to Lyman series?
To n=1
To n=2
To n=3
To n=4
Explanation - Lyman series consists of transitions from higher levels to the ground state (n=1).
Correct answer is: To n=1
Q.9 The first member of the Balmer series in hydrogen corresponds to transition:
3 → 2
2 → 1
4 → 2
5 → 2
Explanation - Balmer series corresponds to transitions ending at n=2. The first member is 3→2.
Correct answer is: 3 → 2
Q.10 Which isotope is used in nuclear fission reactors as fuel?
U-235
U-238
Th-232
C-14
Explanation - Uranium-235 is a fissile isotope used in nuclear reactors and atomic bombs.
Correct answer is: U-235
Q.11 Binding energy per nucleon is maximum for:
Uranium
Iron
Helium
Hydrogen
Explanation - Iron has the highest binding energy per nucleon, making it the most stable element.
Correct answer is: Iron
Q.12 Nuclear fission is:
Splitting of heavy nucleus
Joining of two nuclei
Emission of alpha particles
Decay of a neutron
Explanation - In nuclear fission, a heavy nucleus splits into lighter nuclei, releasing energy.
Correct answer is: Splitting of heavy nucleus
Q.13 Nuclear fusion requires:
Low temperature
High temperature
Catalyst
Magnetic field only
Explanation - Fusion requires extremely high temperature to overcome electrostatic repulsion between nuclei.
Correct answer is: High temperature
Q.14 Alpha particle is:
Electron
Helium nucleus
Proton
Neutron
Explanation - An alpha particle is a Helium nucleus consisting of 2 protons and 2 neutrons.
Correct answer is: Helium nucleus
Q.15 The half-life of a radioactive element is the time in which:
All atoms decay
Half the atoms decay
One atom decays
Decay constant becomes half
Explanation - Half-life is the time required for half the radioactive atoms to decay.
Correct answer is: Half the atoms decay
Q.16 The unit of radioactivity is:
Joule
Curie
Newton
Tesla
Explanation - Curie (Ci) is a unit of radioactivity, though Becquerel (Bq) is SI unit.
Correct answer is: Curie
Q.17 Which radiation has the highest penetrating power?
Alpha
Beta
Gamma
Neutron
Explanation - Gamma rays have the highest penetration ability, requiring thick lead shielding.
Correct answer is: Gamma
Q.18 The decay constant λ is related to half-life (T1/2) as:
λ = ln2 / T1/2
λ = T1/2 / ln2
λ = ln2 × T1/2
λ = 1 / T1/2
Explanation - The relation is λ = ln2 / T1/2, where λ is decay constant.
Correct answer is: λ = ln2 / T1/2
Q.19 Which process powers the sun?
Nuclear fission
Nuclear fusion
Radioactive decay
Chemical reactions
Explanation - The Sun’s energy comes from nuclear fusion of hydrogen into helium.
Correct answer is: Nuclear fusion
Q.20 Which series of hydrogen spectrum lies in the visible region?
Lyman
Balmer
Paschen
Brackett
Explanation - Balmer series corresponds to transitions ending at n=2, visible region.
Correct answer is: Balmer
Q.21 Which quantum number specifies the size of orbit?
Principal
Azimuthal
Magnetic
Spin
Explanation - The principal quantum number (n) defines size and energy of the orbital.
Correct answer is: Principal
Q.22 Which nucleus is most stable?
U-235
Fe-56
C-14
H-1
Explanation - Iron-56 is the most stable nucleus due to maximum binding energy per nucleon.
Correct answer is: Fe-56
Q.23 Radioactive decay is governed by:
Newton’s laws
Laws of probability
Ohm’s law
Conservation of momentum
Explanation - Decay of individual nuclei is random and follows probability laws.
Correct answer is: Laws of probability
Q.24 Which equation relates mass defect to binding energy?
E = mc²
F = ma
pV = nRT
E = hf
Explanation - Binding energy is obtained from mass defect using Einstein’s equation E=mc².
Correct answer is: E = mc²
Q.25 Beta-minus decay converts:
Proton → Neutron
Neutron → Proton
Electron → Positron
Photon → Electron
Explanation - In β⁻ decay, a neutron converts into a proton, emitting an electron and antineutrino.
Correct answer is: Neutron → Proton