CBSE Class 12 Physics Nuclei MCQs Set D

Question: The mass number of He is 4 and that of sulphur is 32. The radius of sulphur nucleus is larger than that of helium by the factor of
(a) 4
(b) 2
(c) √8
(d) 8 
Answer: b

Question: The energy required to break one bond in DNA is 10^–20 J. This value in eV is nearly
(a) 6
(b) 0.6
(c) 0.06
(d) 0.006
Answer: c

Question: The rate of radioactive disintegration at an instant for a radioactive sample of half life 2.2 × 10⁹ s is 10¹⁰ s^–1. The number of radioactive atoms in the sample at that instant is,
(a) 3.17 × 10²⁰
(b) 3.17 × 10¹⁷
(c) 3.17 × 10¹⁸
(d) 3.17 × 10¹⁹
Answer: d

Question: The radius of germanium (Ge) nuclide is measured to be twice the radius of ₄⁹Be. The number of nucleons in Ge are
(a) 72
(b) 73
(c) 74
(d) 75
Answer: a

Question: After 1a and 2β-emissions
(a) mass number reduces by 6
(b) mass number reduces by 4
(c) mass number reduces by 2
(d) atomic number remains unchanged
Answer: b,d

Question: A nucleus of uranium decays at rest into nuclei of thorium and helium. Then
(a) The helium nucleus has more momentum than the thorium nucleus.
(b) The helium nucleus has less kinetic energy than the thorium nucleus.
(c) The helium nucleus has more kinetic energy than the thorium nucleus.
(d) The helium nucleus has less momentum than the thorium nucleus.
Answer: c

Question: Which one of the following pairs of nuclei are isotones?
(a) ₃₄Se⁷⁴, ₃₁Ga⁷¹
(b) ₃₈Sr⁸⁴, ₃₈Sr⁸⁶
(c) ₄₂Mo⁹², ₄₀Zr⁹²
(d) ₂₀Ca⁴⁰, ₁₆S³²
Answer: a

Question: For a radioactive material, half-life is 10 minutes. If initially there are 600 number of nuclei, the time taken (in minutes) for the disintegration of 450 nuclei is
(a) 20
(b) 10
(c) 30
(d) 15
Answer: a

Question: A radioisotope X with a half life 1.4 × 10⁹ years decays to Y which is stable. A sample of the rock from a cave was found to contain X and Y in the ratio 1 : 7. The age of the rock is
(a) 1.96 × 10⁹ years
(b) 3.92 × 10⁹ years
(c) 4.20 × 10⁹ years
(d) 8.40 × 10⁹ years
Answer: c

Question: For the given reaction, the particle X is ₆C¹¹ → ₅B¹¹ + b⁺ + X
(a) neutron
(b) anti neutrino
(c) neutrino
(d) proton
Answer: c

Question: The half life of a radioactive nucleus is 50 days. The time interval (t₂ – t₁) between the time t₂ when 2/3 of it has decayed and the time t₁ when 1/3 of it had decayed is
(a) 30 days
(b) 50 days
(c) 60 days
(d) 15 days
Answer: b

Question: Half life of a radioactive element is 12.5 hours and its quantity is 256 g. After how much time its quantity will remain1 g?
(a) 50 hrs
(b) 100 hrs
(c) 150 hrs
(d) 200 hrs
Answer: b

Question: A sample of radioactive element containing 4 × 10¹⁶ active nuclei. Half life of element is 10 days, then number of decayed nuclei after 30 days
(a) 0.5 × 10¹⁶
(b) 2 × 10¹⁶
(c) 3.5 × 10¹⁶
(d) 1 × 10¹⁶ 
Answer: c

Question: The half life of a radioactive isotope ‘X’ is 20 years. It decays to another element ‘Y’ which is stable. The two elements ‘X’ and ‘Y’ were found to be in the ratio 1 : 7 in a sample of a given rock. The age of the rock is estimated to be
(a) 80 years
(b) 100 years
(c) 40 years
(d) 60 years
Answer: d

Question: Alpha particles are
(a) neutrally charged
(b) positron
(c) protons
(d) ionized helium atoms
Answer: d

Question: A nucleus ruptures into two nuclear parts, which have their velocity ratio equal to 2 : 1. What will be the ratio of their nuclear size (nuclear radius)?
(a) 3^1/2 : 1
(b) 1 : 3^1/2
(c) 2^1/3 : 1
(d) 1 : 2^1/3 
Answer: d

Question: A radioactive nucleus of mass M emits a photon of frequency u and the nucleus recoils. The recoil energy will be
(a) Mc² – hu
(b) h²u²/2Mc²
(c) zero
(d) hu
Answer: b

Question: In a radioactive material the activity at time t₁ is R₁ and at a later time t₂, it is R₂. If the decay constant of the material is λ, then
(a) R₁ = R₂
(b) R₁ R₂e ^-λ(t₁^{− t}₂⁾
(c) R₁ R₂e^λ(t₁ ^{- t}₂⁾
(d) R₁ = R₂(t₂/t₁) 
Answer: b

Question: Two radioactive nuclei P and Q, in a given sample decay into a stable nucleus R. At time t = 0, number of P species are 4 N₀ and that of Q are N0 . Half-life of P (for conversion to R) is 1 minute where as that of Q is 2 minutes. Initially there are no nuclei of R present in the sample. When number of nuclei of P and Q are equal, the number of nuclei of R present in the sample would be
(a) 2 N₀
(b) 3 N₀
(c) 9N₀/2
(d) 5N₀/2
Answer: c

Question: Two radioactive materials X₁ and X₂ have decay constants 5λ and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X₁ to that X₂ will be 1/e after a time
(a) 1/4λ
(b) e/λ
(c) λ
(d) 1/2λ
Answer: a

Question: The energy equivalent of 0.5 g of a substance is
(a) 4.5 × 10¹⁶ J
(b) 4.5 × 10¹³ J
(c) 1.5 × 10¹³ J
(d) 0.5 × 10¹³ J
Answer: b

Question: a-particles, b-particles and g-rays are all having same energy. Their penetrating power in a given medium in increasing order will be
(a) Υ, a, b
(b) a, b, Υ
(c) b, a, Υ
(d) b, Υ, a
Answer: b

Question: A nucleus represented by the symbol ^A_ZX has
(a) Z neutrons and A – Z protons
(b) Z protons and A – Z neutrons
(c) Z protons and A neutrons
(d) A protons and Z – A neutrons
Answer: b

Question: If the nuclear force between two protons, two neutrons and between proton and neutron is denoted by F_pp, F_nn and F_pn respectively, then
(a) F_pp ≈ F_nn ≈ F_pn
(b) F_pp ≠ F_nn and F_pp = F_nn
(c) F_pp = F_nn = F_pn
(d) F_pp ≠ F_nn ≠ F_pn 
Answer: c

Question: In a radioactive decay process, the negatively charged emitted b-particles are
(a) the electrons produced as a result of the decay of neutrons inside the nucleus
(b) the electrons produced as a result of collisions between atoms
(c) the electrons orbiting around the nucleus
(d) the electrons present inside the nucleus.
Answer: a

Question: Radioactive material ‘A’ has decay constant ‘8 l’ and material ‘B’ has decay constant ‘l’. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material ‘B’ to that ‘A’ will be (1/e)?
(a) 1/7λ
(b) 1/8λ
(c) 1/9λ
(d) 1/λ
Answer: b

Question: Two radioactive substances A and B have decay constants 5l and l respectively. At t = 0 they have the same number of nuclei. The ratio of number of nuclei of A to those of B will be (1/e)2 after a time interval
(a) 4λ
(b) 2λ
(c) 1/2λ
(d) 1/4λ
Answer: a

Question: The energy equivalent of one atomic mass unit is
(a) 1.6 × 10^–19 J
(b) 6.02 × 10²³ J
(c) 931 MeV
(d) 9.31 MeV 
Answer: c

Question: Which rays contain (positive) charged particles?
(a) α-rays
(b) β-rays
(c) y-rays
(d) X-rays
Answer: a

Question: In the reaction ₁²H +₃¹H → ₄²He + ¹₀n, if the binding energies of ₁²H, ₃¹H and ₂⁴He are respectively a, b and c (in MeV), then the energy (in MeV) released in this reaction is
(a) a + b + c
(b) a + b – c
(c) c – a – b
(d) c + a – b
Answer: c

Question: The mass number of a nucleus is
(a) always less than its atomic number
(b) always more than its atomic number
(c) sometimes equal to its atomic number
(d) sometimes less than and sometimes more than its atomic number
Answer: c

Question: A deutron is bombarded on ₈O¹⁶ nucleus then a-particle is emitted. The product nucleus is
(a) ₇N¹³
(b) ₅B¹⁰
(c) ₄Be⁹
(d) ₇N¹⁴
Answer: d

Question: X(n, a) ₃⁷Li, then X will be
(a) ₅¹⁰B
(b) ₅⁹B
(c) ₄¹¹Be
(d) ₂⁴He
Answer: a

Question: The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an
(a) isomer of parent
(b) isotone of parent
(c) isotope of parent
(d) isobar of parent 
Answer: c

Question: A sample of radioactive element has a mass of 10 g at an instant t = 0. The approximate mass of this element in the sample after two mean lives is
(a) 1.35 g
(b) 2.50 g
(c) 3.70 g
(d) 6.30 g
Answer: a

Question: If M(A; Z), M_p and M_n denote the masses of the nucleus _A^ZX, proton and neutron respectively in units of u (1 u = 931.5 MeV/c²) and BE represents its binding energy in MeV, then
(a) M(A, Z) = ZM_p + (A – Z)M_n – BE
(b) M(A, Z) = ZM_p + (A – Z)M_n + BE/c²
(c) M(A, Z) = ZM_p + (A – Z)M_n – BE/c²
(d) M(A, Z) = ZM_p + (A – Z)M_n + BE 
Answer: c