JEE Physics Nuclei MCQs Set 27

Multiple Choice Questions (MCQs) for JEE Physics: Nuclei

Access targeted multiple-choice questions for Nuclei designed to align with the latest JEE academic syllabus for JEE Physics. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.

Practice Nuclei MCQs for JEE Physics

View or download the dedicated Nuclei MCQ resource below. Practicing these 50 objective questions regularly builds familiarity with standard exam patterns and helps secure higher marks in final Physics evaluations.

Multiple Choice Questions

Question 1: The half-life period and the mean life period of a radioactive element are denoted respectively by Th and Tm. Then
(a) Th = Tm
(b) Th > Tm
(c) Th < Tm
(d) Th ≥ Tm
Show Answer & Explanation

Answer: (c) Th < Tm

Explanation:
1. Th = 0.693Tm, so Th < Tm.

Teacher's Note:
1. Recall the basic fact.

Question 2: Particles which can be added to the nucleus of an atom without changing its chemical properties are called
(a) neutrons
(b) electrons
(c) protons
(d) alpha particles
Show Answer & Explanation

Answer: (a) neutrons

Explanation:
1. Chemical properties depend on the atomic number (protons), so adding neutrons does not change them.

Teacher's Note:
1. Recall the basic fact.

Question 3:
Assertion (A): ZXᴬ undergoes 2α, 2β⁻ particles and 2γ-rays, the daughter product is Z₋₂Yᴬ⁻⁸.
Reason (R): In α-decay the mass number decreases by 4 and atomic number decreases by 2. In β-decay the mass number remains unchanged, but atomic number increases by 1.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Two α: \( A - 8, Z - 4 \). Two β⁻: \( Z + 2 \).
2. Net: \( A - 8 \) and \( Z - 2 \), using the rules in the reason.

Teacher's Note:
1. Compare the two statements.

Question 4: At any instant, the ratio of the amount of radioactive substances is 2 : 1. If their half lives are respectively 12 and 16 hours, then after two days, what will be the ratio of the substances?
(a) 1 : 1
(b) 2 : 1
(c) 1 : 2
(d) 1 : 4
Show Answer & Explanation

Answer: (a) 1 : 1

Explanation:
1. \( 48 h \) is 4 half-lives of the first (\( 2/16 = 1/8 \) of the unit) and 3 half-lives of the second (1/8).
2. The ratio is 1 : 1.

Teacher's Note:
1. Recall the basic fact.

Question 5: The activity of a radioactive sample is measured as N₀ counts per minute at t = 0 and N₀/e counts per minute at t = 5 minutes. The time (in minutes) at which the activity reduces to half its value is
(a) \( \log_e2/5 \)
(b) \( \frac{5}{\log_e2} \)
(c) \( 5\log_{10}2 \)
(d) \( 5\log_e2 \)
Show Answer & Explanation

Answer: (d) \( 5\log_e2 \)

Explanation:
1. \( e^{-5\lambda} = 1/e \) gives \( \lambda = 1/5 \) per minute.
2. \( t\frac{1}{2} = \ln2/\lambda = 5 \ln2 \).

Teacher's Note:
1. Recall the basic fact.

Question 6: If a radioactive element is placed in an evacuated chamber, then the rate of radioactive decay will
(a) decrease
(b) remain unchanged
(c) increase
(d) none of these
Show Answer & Explanation

Answer: (b) remain unchanged

Explanation:
1. Decay is independent of external conditions such as pressure.

Teacher's Note:
1. Recall the basic fact.

Question 7: The electrons cannot exist inside the nucleus because
(a) de-Broglie wavelength associated with electron in β-decay is much less than the size of nucleus
(b) de-Broglie wavelength associated with electron in β-decay is much greater than the size of nucleus
(c) de-Broglie wavelength associated with electron in β-decay is equal to the size of nucleus
(d) negative charge cannot exist in the nucleus
Show Answer & Explanation

Answer: (b) de-Broglie wavelength associated with electron in β-decay is much greater than the size of nucleus

Explanation:
1. An electron with the energy seen in β-decay has a de Broglie wavelength far larger than the nucleus, so it cannot be confined inside.

Teacher's Note:
1. Recall the basic fact.

Question 8:
Assertion (A): It is not possible to use ³⁵Cl as the fuel for fusion energy.
Reason (R): The binding energy of ³⁵Cl is too small.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. Fusion releases energy only for light nuclei (\( A \) below about 56).
2. ³⁵Cl is already near the peak of binding energy per nucleon and its binding energy is large, so the reason is false.

Teacher's Note:
1. Compare the two statements.

Question 9: Fusion reactions take place at high temperature because
(a) atoms are ionised at high temperature
(b) molecules break up at high temperature
(c) nuclei break up at high temperature
(d) kinetic energy is high enough to overcome repulsion between nuclei
Show Answer & Explanation

Answer: (d) kinetic energy is high enough to overcome repulsion between nuclei

Explanation:
1. High kinetic energy is needed to overcome the Coulomb barrier.

Teacher's Note:
1. Recall the basic fact.

Question 10: A nuclear reaction ZXᴬ → Z₊₁Yᴬ + ₋₁e⁰ + ν̄ represents
(a) fission
(b) β-decay
(c) σ-decay
(d) fusion
Show Answer & Explanation

Answer: (b) β-decay

Explanation:
1. Emission of an electron and an antineutrino with \( Z \) increasing by 1 is β⁻ decay.

Teacher's Note:
1. Recall the basic fact.

Question 11:
Assertion (A): Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason (R): For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei it decreases with increasing Z.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (c) A is true, but R is false.

Explanation:
1. Both processes move towards higher binding energy per nucleon, so the assertion is true.
2. For heavy nuclei \( B/A \) decreases with \( Z \) and for light nuclei it increases, so the reason is false.

Teacher's Note:
1. Compare the two statements.

Question 12: Control rods used in nuclear reactors are made of
(a) stainless steel
(b) graphite
(c) plutonium
(d) cadmium
Show Answer & Explanation

Answer: (d) cadmium

Explanation:
1. Cadmium (or boron) absorbs neutrons strongly.

Teacher's Note:
1. Recall the basic fact.

Question 13: Charge on an α-particle is
(a) 1.6 × 10⁻¹⁹ C
(b) 3.2 × 10⁻¹⁹ C
(c) 1.6 × 10⁻²⁰ C
(d) 4.8 × 10⁻¹⁹ C
Show Answer & Explanation

Answer: (b) 3.2 × 10⁻¹⁹ C

Explanation:
1. An α-particle is He²⁺: \( q = 2e = 3.2 \times 10^{-19} C \).

Teacher's Note:
1. Recall the basic fact.

Question 14: An archaeologist analyses the wood in a prehistoric structure and finds that C¹⁴ (half life = 5700 years) to C¹² is only one-fourth of that found in the cells of buried plants. The age of the wood is about
(a) 5700 years
(b) 2850 years
(c) 11,400 years
(d) 22,800 years
Show Answer & Explanation

Answer: (c) 11,400 years

Explanation:
1. One-fourth means 2 half-lives = 11,400 years.

Teacher's Note:
1. Recall the basic fact.

Question 15: A freshly prepared radioactive source of half life 2 hr emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is
(a) 6 hr
(b) 12 hr
(c) 24 hr
(d) 128 hr
Show Answer & Explanation

Answer: (b) 12 hr

Explanation:
1. \( 64 = 2^{6} \), so 6 half-lives are required: \( 6 \times 2 = 12 \) hr.

Teacher's Note:
1. Recall the basic fact.

Question 16:
Assertion (A): The binding energy per nucleon, for nuclei with atomic mass number A > 100, decreases with A.
Reason (R): The forces are weak for heavier nuclei.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.
Show Answer & Explanation

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. In heavy nuclei the nuclear forces are weaker on average because of long-range Coulomb repulsion between protons.
2. So \( B/A \) decreases.

Teacher's Note:
1. Think about Coulomb repulsion in large nuclei.

Question 17: If radius of the ²⁷₁₃Al nucleus is estimated to be 3.6 fermi then the radius of ¹²⁵₅₂Te nucleus be nearly
(a) 8 fermi
(b) 6 fermi
(c) 5 fermi
(d) 4 fermi
Show Answer & Explanation

Answer: (b) 6 fermi

Explanation:
1. \( R ∝ A^{1}/3 \)).
2. R = 3.6 × (125/27)¹/3) = 3.6 × 5/3 = 6 fermi.

Teacher's Note:
1. Recall the basic fact.

Question 18: The activity of a freshly prepared radioactive sample is 10¹⁰ disintegrations per second, whose mean life is 10⁹ s. The mass of an atom of this radioisotope is 10⁻²⁵ kg. The mass (in mg) of the radioactive sample is
(a) 1
(b) 3
(c) 5
(d) 6
Show Answer & Explanation

Answer: (a) 1

Explanation:
1. \( N = A \) × τ = \( 10^{10} \times 10^{9} = 10^{19} \) atoms.
2. Mass = \( 10^{19} \times 10^{-25} = 10^{-6} \) kg = 1 mg.

Teacher's Note:
1. Recall the basic fact.

Question 19: A mixture consists of two radioactive materials A₁ and A₂ with half lives of 20 s and 10 s respectively. Initially the mixture has 40 g of A₁ and 160 g of A₂. The amount of the two in the mixture will become equal after
(a) 60 s
(b) 80 s
(c) 20 s
(d) 40 s
Show Answer & Explanation

Answer: (d) 40 s

Explanation:
1. \( 40 \times 2^{-t/20} = 160 \times 2^{-t/10} \).
2. \( 2^{t/20} = 4 \), so \( t = 40 s \).

Teacher's Note:
1. Recall the basic fact.

Question 20: For a nuclear fusion process, suitable nuclei are
(a) any nuclei
(b) heavy nuclei
(c) lighter nuclei
(d) nuclei lying in the middle of periodic table
Show Answer & Explanation

Answer: (c) lighter nuclei

Explanation:
1. Light nuclei fuse to give more tightly bound nuclei and release energy.

Teacher's Note:
1. Recall the basic fact.

Question 21: Which of the following statements is not true regarding Einstein's mass energy relation?
(a) Mass disappears to reappear as energy.
(b) Energy disappears to reappear as mass.
(c) Mass and energy are two different forms of the same entity.
(d) Mass and energy can never be related to each other.
Show Answer & Explanation

Answer: (d) Mass and energy can never be related to each other.

Explanation:
1. Mass and energy are related by \( E \) = mc², so the last statement is false.

Teacher's Note:
1. Recall the basic fact.

Question 22: The radioactivity of a sample is R₁ at a time T₁ and R₂ at a time T₂. If the half-life of the specimen is T, then the number of atoms that have disintegrated in the time (T₁ − T₂) is proportional to
(a) \( (R_1T_1-R_2T_2) \)
(b) \( (R_1-R_2) \)
(c) \( (R_1-R_2)/T \)
(d) \( (R_1-R_2)T \)
Show Answer & Explanation

Answer: (d) \( (R_1-R_2)T \)

Explanation:
1. \( R = \lambdaN \), so atoms decayed = \( (R_{1} - R_{2})/\lambda \).
2. Since \( 1/\lambda = T/0.693 \), this is proportional to \( (R_{1} - R_{2})T \).

Teacher's Note:
1. Recall the basic fact.

Question 23: The mass defect in a particular nuclear reaction is 0.3 grams. The amount of energy liberated in kilowatt hour is (Velocity of light = 3 × 10⁸ m/s)
(a) 1.5 × 10⁶
(b) 2.5 × 10⁶
(c) 3 × 10⁶
(d) 7.5 × 10⁶
Show Answer & Explanation

Answer: (d) 7.5 × 10⁶

Explanation:
1. \( E = \Deltam c^{2} = 3 \times 10^{-4} \times 9 \times 10^{16} = 2.7 \times 10^{13} J \).
2. In kWh: \( 2.7 \times 10^{13}/3.6 \times 10^{6} = 7.5 \times 10^{6} \).

Teacher's Note:
1. Recall the basic fact.

Question 24: The mass number of He is 4 and that for sulphur is 32. The radius of sulphur nuclei is larger than that of helium by
(a) \( \sqrt8 \)
(b) \( 4 \)
(c) \( 2 \)
(d) \( 8 \)
Show Answer & Explanation

Answer: (c) \( 2 \)

Explanation:
1. \( R ∝ A^{1}/3 \)).
2. R_S/R_He = (32/4)¹/3) = 2.

Teacher's Note:
1. Recall the basic fact.

Question 25: Half life of radioactive element depends upon
(a) amount of element present
(b) temperature
(c) pressure
(d) nature of element
Show Answer & Explanation

Answer: (d) nature of element

Explanation:
1. Half-life is a property of the nuclide only.

Teacher's Note:
1. Recall the basic fact.

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