JEE Physics Nuclei MCQs Set 28

Download JEE 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.

Chapter-wise Objective Questions: Nuclei

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 number of protons in an atom of atomic number Z and mass number A is
(a) zero
(b) Z
(c) A − Z
(d) A
Show Answer & Explanation

Answer: (b) Z

Explanation:
1. The atomic number equals the number of protons.

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

Question 2: In which sequence the radioactive radiations are emitted in the nuclear reaction ZXᴬ → Z₊₁Yᴬ → Z₋₁Kᴬ⁻⁴?
(a) γ and β
(b) α and γ
(c) β and α
(d) β and γ
Show Answer & Explanation

Answer: (c) β and α

Explanation:
1. The first step raises \( Z \) by 1 at constant \( A (\beta^{-}) \).
2. The second step lowers \( A \) by 4 and \( Z \) by 2 (α).

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

Question 3: A radioactive material undergoes decay by ejecting electrons. The electron ejected in this process is
(a) the electron from the decay of a neutron
(b) the electron present in the nucleus
(c) the resulting from the conversion of γ photon
(d) an orbital electron
Show Answer & Explanation

Answer: (a) the electron from the decay of a neutron

Explanation:
1. In β⁻ decay a neutron changes to a proton, an electron and an antineutrino.

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

Question 4: Nuclear forces exist between
(a) neutron - neutron
(b) proton - proton
(c) neutron - proton
(d) all of these
Show Answer & Explanation

Answer: (d) all of these

Explanation:
1. Nuclear force is charge independent and acts between any pair of nucleons.

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

Question 5: The nuclear radius is of the order of
(a) 10⁻¹⁰ m
(b) 10⁻⁶ m
(c) 10⁻¹⁵ m
(d) 10⁻¹⁴ m
Show Answer & Explanation

Answer: (c) 10⁻¹⁵ m

Explanation:
1. \( R = R_{0}A^{1}/3 \)) with \( R_{0} \approx 1.2 \times 10^{-15} m \), so the nuclear radius is about \( 10^{-15} m \).

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

Question 6: The half-life of radioactive Radon is 3.8 days. The time at the end of which (1/20)th of the Radon sample will remain undecayed is (given log₁₀e = 0.4343)
(a) 13.8 days
(b) 16.5 days
(c) 33 days
(d) 76 days
Show Answer & Explanation

Answer: (b) 16.5 days

Explanation:
1. \( N/N_{0} = 1/20 = 2^{-n}, n = \log_{2}20 = 4.32 \).
2. \( t = 4.32 \times 3.8 = 16.4 \) days ≈ 16.5 days.

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

Question 7: Three specimens A, B, C of same radioactive element have activities 1 microcurie, 1 rutherford and 1 becquerel respectively. Which specimen has maximum mass?
(a) A
(b) B
(c) C
(d) all have equal masses
Show Answer & Explanation

Answer: (b) B

Explanation:
1. 1 μCi = 3.7 × 10⁴ Bq, 1 rutherford = 10⁶ Bq and 1 Bq = 1 decay/s.
2. For the same element the mass is proportional to the activity, so \( B \) is largest.

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

Question 8: If N₀ is the original mass of the substance of half-life period t½ = 5 years, then the amount of substance left after 15 years is
(a) \( N_0/8 \)
(b) \( N_0/16 \)
(c) \( N_0/2 \)
(d) \( N_0/4 \)
Show Answer & Explanation

Answer: (a) \( N_0/8 \)

Explanation:
1. 15 years = 3 half-lives, so \( N = N_{0}/8 \).

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

Question 9: Artificial radioactivity was discovered by
(a) Klaproth
(b) Rontgen
(c) Irene Curie and Joliot
(d) P. Curie and M. Curie
Show Answer & Explanation

Answer: (c) Irene Curie and Joliot

Explanation:
1. Irene Curie and Joliot discovered artificial radioactivity in 1934.

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

Question 10: When a U²³⁸ nucleus originally at rest, decays by emitting an alpha particle having a speed u, the recoil speed of the residual nucleus is
(a) \( \frac{4u}{238} \)
(b) \( -\frac{4u}{234} \)
(c) \( \frac{4u}{234} \)
(d) \( -\frac{4u}{238} \)
Show Answer & Explanation

Answer: (c) \( \frac{4u}{234} \)

Explanation:
1. The daughter nucleus has mass number 234.
2. \( 4u = 234 V \), so the recoil speed is \( 4u/234 \).

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

Question 11: The radius of a nucleus is
(a) directly proportional to its mass number
(b) inversely proportional to its atomic weight
(c) directly proportional to the cube root of its mass number
(d) None of these
Show Answer & Explanation

Answer: (c) directly proportional to the cube root of its mass number

Explanation:
1. \( R = R_{0}A^{1}/3 \)).

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

Question 12: The binding energies per nucleon for a deuteron and an α-particle are x₁ and x₂ respectively. What will be the energy Q released in the reaction ²₁H + ²₁H → ⁴₂He + Q?
(a) \( 4(x_1+x_2) \)
(b) \( 4(x_2-x_1) \)
(c) \( 2(x_1+x_2) \)
(d) \( 2(x_2-x_1) \)
Show Answer & Explanation

Answer: (b) \( 4(x_2-x_1) \)

Explanation:
1. Binding energy of He = \( 4x_{2} \) and of two deuterons = \( 2 \times 2x_{1} = 4x_{1} \).
2. \( Q = 4x_{2} - 4x_{1} = 4(x_{2} - x_{1}) \).

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

Question 13:
Assertion (A): Radioactivity of 10⁸ undecayed radioactive nuclei of half life of 50 days is equal to that of 1.2 × 10⁸ number of undecayed nuclei of some other material with half life of 60 days.
Reason (R): Radioactivity is proportional to half-life.
(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. Activity = \( 0.693N/T\frac{1}{2} \): \( 10^{8}/50 = 2 \times 10^{6} \) and \( 1.2 \times 10^{8}/60 = 2 \times 10^{6} \), so they are equal and the assertion is true.
2. Activity is inversely proportional to half-life, so the reason is false.

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

Question 14: After 150 days, the activity of a radioactive sample is 5000 dps. The activity becomes 2500 dps after another 75 days. Initially the activity of the sample is
(a) 20000 dps
(b) 40000 dps
(c) 7500 dps
(d) 10000 dps
Show Answer & Explanation

Answer: (a) 20000 dps

Explanation:
1. Halving in 75 days gives \( T\frac{1}{2} = 75 \) days.
2. 150 days is 2 half-lives, so the initial activity = \( 5000 \times 4 = 20000 \) dps.

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

Question 15: Radioactive samples are stored in lead boxes because it is
(a) heavy
(b) strong
(c) good absorber
(d) bad conductor
Show Answer & Explanation

Answer: (c) good absorber

Explanation:
1. Lead is a good absorber of the radiation.

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

Question 16: The half life of the radioactive substance is 40 days. The substance will disintegrate completely in
(a) 40 days
(b) 400 days
(c) 4000 days
(d) infinite time
Show Answer & Explanation

Answer: (d) infinite time

Explanation:
1. Exponential decay never reaches exactly zero.

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

Question 17: A radioactive element X converts into another stable element Y. Half life of X is 2 hrs. Initially only X is present. After time t, the ratio of atoms of X and Y is found to be 1 : 4, then t in hours is
(a) 2
(b) between 4 and 6
(c) 8
(d) 6
Show Answer & Explanation

Answer: (b) between 4 and 6

Explanation:
1. \( X \) : \( Y = 1 \) : 4 means \( X \) left = 1/5 of the initial.
2. \( n = \log_{2}5 = 2.32 \) half-lives = 4.64 hours, between 4 and 6.

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

Question 18: Radioactive substance emits
(a) α-rays
(b) β-rays
(c) γ-rays
(d) All of the above
Show Answer & Explanation

Answer: (d) All of the above

Explanation:
1. A radioactive substance can emit α, β and γ radiations (in different decays).

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

Question 19: Match Column I with Column II.
Column IColumn II
(A) Isotopes(1) Mass number same but different atomic number
(B) Isobars(2) Atomic number same but different mass number
(C) Isotones(3) Number of neutrons plus number of protons
(D) Nucleons(4) Number of neutrons same but different atomic number

(a) A-2, B-1, C-4, D-3
(b) A-2, B-4, C-1, D-3
(c) A-1, B-2, C-4, D-3
(d) A-3, B-1, C-4, D-2
Show Answer & Explanation

Answer: (a) A-2, B-1, C-4, D-3

Explanation:
1. Isotopes: same \( Z \).
2. Isobars: same \( A \).
3. Isotones: same \( N \).
4. Nucleons: protons plus neutrons.

Teacher's Note:
1. Recall the definitions.

Question 20: In the uranium radioactive series, the initial nucleus is ⁹²U²³⁸ and that the final nucleus is ⁸²Pb²⁰⁶. When uranium nucleus decays to lead, the number of α particles and β particles emitted are
(a) 8α, 6β
(b) 6α, 7β
(c) 6α, 8β
(d) 4α, 3β
Show Answer & Explanation

Answer: (a) 8α, 6β

Explanation:
1. Mass number falls by 32, so 8 α-particles.
2. Charge falls by 16 from α but only 10 overall, so 6 β⁻ particles are emitted.

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

Question 21: An element A decays into an element C by a two step process: A → B + ²He⁴ and B → C + 2e⁻. Then
(a) A and C are isotopes
(b) A and C are isobars
(c) A and B are isotopes
(d) A and B are isobars
Show Answer & Explanation

Answer: (a) A and C are isotopes

Explanation:
1. After one α and two \( \beta^{-}, Z \) returns to its original value while \( A \) decreases by 4.
2. Same \( Z \), different \( A \): isotopes.

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

Question 22: The mass of an atomic nucleus is less than the sum of the masses of its constituents. This mass defect is converted into
(a) heat energy
(b) light energy
(c) electrical energy
(d) energy which binds nucleons
Show Answer & Explanation

Answer: (d) energy which binds nucleons

Explanation:
1. The mass defect appears as the binding energy that holds the nucleons together.

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

Question 23:
Assertion (A): Neutrons penetrate matter more readily as compared to protons.
Reason (R): Neutrons are slightly more massive than protons.
(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: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Neutrons are uncharged and so are not repelled by nuclei.
2. The mass fact is true but is not the reason.

Teacher's Note:
1. Penetration is due to zero charge.

Question 24: The same radioactive nucleus may emit
(a) all the three α, β and γ one after another
(b) all the three α, β and γ radiations simultaneously
(c) only α and β simultaneously
(d) only one α, β and γ at a time
Show Answer & Explanation

Answer: (d) only one α, β and γ at a time

Explanation:
1. A nucleus emits only one kind of particle at a time in a given decay (γ may follow).

Teacher's Note:
1. One decay event gives one type of emission.

Question 25: The process of radioactive radiations remains unaffected due to
(a) physical changes
(b) chemical changes
(c) electric or magnetic fields
(d) all of the above
Show Answer & Explanation

Answer: (d) all of the above

Explanation:
1. Radioactivity is a nuclear process, independent of all these external conditions.

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

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