CBSE Class 12 Physics Nuclei MCQs Set B

Question. In the nuclear reaction, there is a conservation of:
(a) momentum
(b) mass
(c) energy
(d) all of these

Answer : A

Question. If the radioactive decay constant of radium is 1.07 × 10^–4 per year. Then its half life period approximately is equal to:
(a) 5000 years
(b) 6500 years
(c) 7000 years
(d) 8900 years

Answer : B

Question. In ₈₈Ra²²⁶ nucleus there are : 
(a) 226 protons and 88 electrons
(b) 138 protons and 88 neutrons
(c) 226 neutrons and 138 electrons
(d) 138 neutrons and 88 protons

Answer : D

Question. The activity of radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes, the decay constant is approximately :
(a) 0.922 per minute
(b) 0.270 per minute
(c) 0.461 per minute
(d) 0.39 per minute

Answer : C

Question. The activity of a radioactive sample is 1.6 curie and its half life is 2.5 days. Then activity after 10 days will be :
(a) 0.16 curie
(b) 0.8 curie
(c) 0.1 curie
(d) 0.4 curie

Answer : C

Question. Which one of the following is used as a moderator in nuclear reaction ?
(a) Uranium
(b) Heavy water
(c) Cadmium
(d) Plutonium

Answer : B

Question. In an atom bomb, the energy is released because of the :
(a) chain reaction of neutrons and ₉₂U²³⁸
(b) chain reaction of neutrons and ₉₂U²³⁵
(c) chain reaction of neutrons and ₉₂U²³⁶
(d) chain reaction of neutrons and ₉₂U²⁴⁰

Answer : B

Question. A radioactive substance decays to 1/16th of its initial activity in 40 days. The half-life of the radioactive substance expressed in days is
(a) 2.5
(b) 5
(c) 10
(d) 20

Answer : C

Question. Nuclear fusion is possible
(a) only between light nuclei
(b) only between heavy nuclei
(c) between both light and heavy nuclei
(d) only between nuclei which are stable against b-decay

Answer : A

Question. Radioactive nuclei that are injected into a potient collected at certain sites within its body, undergoing radioactive decay and emitting electromagnetic radiation. These radiations can then be recorded by a detector. This procedure provides an important diagnostic tools called
(a) Gamma camera
(b) CAT can
(c) Radiotracer technique
(d) Gamma ray spectroscopy

Answer : C

Question. In a material medium, when a positron meets an electron both the particles annihilate leading to the emission of two gamma ray photons. This process forms the basis of an important diagnostic procedure called
(a) MRI
(b) PET
(c) CAT
(d) SPECT

Answer : B

Question. Calculate power output of ²³⁵₉₂U reactor, if it takes 30 days to use up 2 kg of fuel, and if each fission gives 185 MeV of useable energy. Avogadro’s number = 6 × 10²³ /mol?
(a) 56.3 MW
(b) 60.3 MW
(c) 58.3 MW
(d) 54.3 MW

Answer : C

Question. Starting with a sample of pure ⁶⁶Cu,7/8 of it decays into Zn in 15 minutes. The corresponding half life is 
(a) 15 minutes
(b) 10 minutes
(c) 7 .1/2 minutes
(d) 5 minutes

Answer : D

Question. A radioactive material decays by simultaneous emission of two particles with respective halflives 1620 and 810 years. The time, in years, after which one-fourth of the material reamins is
(a) 1080
(b) 2430
(c) 3240
(d) 4860

Answer : A

Question. If the binding energy per nucleon of a nuclide is high then
(a) It should be abundantly available in nature
(b) It will decay instantly
(c) It will have a large disintegration constant
(d) It will have a small half-life.

Answer : A

Question. Activity of a radioactive sample decreases to (l/3)rd of its original value in 3 days. Then, in 9 days its activity will become
(a) (1/27) of the original value
(b) (1/9) of the original value
(c) (1/18) of the original value
(d) (1/3) of the original value

Answer : A

Question. The half life of a radioactive substance against a -decay is 1.2 × 10⁷ s. What is the decay rate for 4.0 × 10¹⁵ atoms of the substance
(a) 4.6 × 10 ¹² atoms/s
(b) 2.3 × 10 ¹¹ atoms/s
(c) 4.6 × 10 ¹⁰ atoms/s
(d) 2.3 × 10 ⁸ atoms/s

Answer : D

Question. In the nucleus of ₁₁Na²³, the number of protons, neutrons and electrons are
(a) 11, 12, 0
(b) 23, 12, 11
(c) 12, 11, 0
(d) 23, 11, 12

Answer : A

Question. The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 & 975 counts per minute at T = 5 minutes. The decay constant is approximately.
(a) 0.922 per minutes
(b) 0.691 per minutes
(c) 0.461 per minutes
(d) 0.230 per minutes

Answer : C

Question. A neutron travelling with a velocity v and kinetic energy E has a perfectly elastic head-on collision with a nucleus of an atom of mass number A at rest. The fraction of total energy retained by the neutron is approximately
(a) [(A – 1)/(A + 1)]²
(b) [(A + 1)/(A – 1)]²
(c) [(A – 1)/A]²
(d) [(A + 1)/A]²

Answer : A

Question. Atomic weight of boron is 10.81 and it has two isotopes ₅B¹⁰ and ₅B¹¹. Then ratio of ₅B¹⁰ : ₅B¹¹ in nature would be
(a) 19 : 81
(b) 10 : 11
(c) 15 : 16
(d) 81 : 19

Answer : A

Question. Which of the following statements is true?
(a) ₇₈Pt¹⁹² has 78 neutrons
(b) ₈₄Po²¹⁴ → ₈₂Pb²¹⁰ + β^–
(c) ₉₂U²³⁸ → ₉₀Th²³⁴ + ₂He⁴
(d) ₉₀Th²³⁴ → ₉₁Pa²³⁴ + ₂He⁴

Answer : C

Question. Consider a radioactive material of half-life 1.0 minute. If one of the nuclei decays now, the next one will decay
(a) after 1 minute
(b) after (1/loge2) minute
(c) after 1/N minute, where N is the number of nuclei present at that moment
(d) after any time

Answer : D

Question. The masses of neutron and proton are 1.0087 a.m.u. and 1.0073 a.m.u. respectively. If the neutrons and protons combine to form a helium nucleus (alpha particles) of mass 4.0015 a.m.u the binding energy fo the helium nucleus will be (1 a.m.u. = 931 MeV)
(a) 28.4 MeV
(b) 20.8 MeV
(c) 27.3 MeV
(d) 14.2 MeV

Answer : A

Question. At any instant, the ratio of the amount of radioactive substances is 2 : 1. If their half lives be 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

Answer : A

Question. Half lives of two radio active substance A & B are respectively 20 minutes & 40 minutes. Initially the samples of A & B have equal numbers of nulcei. After 80 minutes the ratio of remaining numbers of A & B nuclei is
(a) 1 : 16
(b) 4 : 1
(c) 1 : 4
(d) 1 : 1

Answer : C

Question. The reaction responsible for the production of light energy from the sun will be:
(a) fission
(b) fusion
(c) nuclear
(d) none of these

Answer : B

Question. Half life of a substance is 20 minutes, then the time between 33 % decay and 67 % decay will be
(a) 20 minute
(b) 40 minute
(c) 50 minute
(d) 10 minute

Answer : A

Question. Consider the following nuclear reaction X200 → A110 + B90 + Energy
If the binding energy per nucleon for X, A and B are 7.4 MeV, and 8.2 MeV and 8.2 MeV respectively, the energy released will be :
(a) 90 MeV
(b) 110 MeV
(c) 200 MeV
(d) 160 MeV

Answer : D

Question. In each fission of ₉₂U²³⁵ releases 200 MeV, how many fissions must occur per second to produce power of 1 kW ? 
(a) 1.25 × 10¹⁸
(b) 3.125 × 10¹³
(c) 3.2 × 10¹⁸
(d) 1.25 × 10¹³

Answer : B

Question. A radioactive material has half-life of 10 days.What fraction of the material would remain after 30 days ?
(a) 0.5
(b) 0.25
(c) 0.125
(d) 0.33

Answer : C

Question. The operation of a nuclear reactor is said to be critical, if the multiplication factor (K) has a value
(a) 1
(b) 1.5
(c) 2.1
(d) 2.5

Answer : A

Question. ²³⁸U has 92 protons and 238 nucleons. It decays by emitting an Alpha particle and becomes
(a) ²³⁴₉₂U
(b) ²³⁴ ₉₀Th
(c) ²³⁵₉₂U
(d) ²³⁷₉₃Np

Answer : B

Question. If Alpha, Beta and Gamma rays carry same momentum, which has the longest wavelength
(a) Alpha rays
(b) Beta rays
(c) Gamma rays
(d) None, all have some wavelength

Answer : D

Question. The fossil bone has a ¹⁴C : ¹²C ratio, which is [1/16] of that in a living animal bone. If the halflife of ¹⁴C is 5730 years, then the age of the fossil bone is 
(a) 11460 years
(b) 17190 years
(c) 22920 years
(d) 45840 years

Answer : C

Question. Which one of the following pairs of nuclei are isotones?
(a) ₃₄Se⁷⁴, ₃₁Ga⁷¹
(b) ₃₈Sr^84, ₃₈Sr⁸⁶
(c) ₄₂Mo⁹², ₄₀Zr⁹²
(d) ₂₀Ca⁴⁰, ₁₆S³²

Answer : A

Question. A nucleus represented by the symbol Z AX 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. 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. The constituents of atomic nuclei are believed to be
(a) neutrons and protons
(b) protons only
(c) electrons and protons
(d) electrons, protons and neutrons

Answer : A

Question. If the radius of a nucleus ²⁵⁶X is 8 fermi, then the radius of ⁴He nucleus will be
(a) 16 fermi
(b) 2 fermi
(c) 32 fermi
(d) 4 fermi

Answer : B

Question. The energy released per fission of a ₉₂U²³⁵ nucleus is nearly
(a) 200 eV
(b) 20 eV
(c) 200 MeV
(d) 2000 eV

Answer : C

Question. Order of magnitude of density of uranium nucleus is (mp = 1.67 × 10^–27 kg)
(a) 10²⁰ kg / m³
(b) 10¹⁷ kg / m³
(c) 10¹⁴ kg / m³
(d) 10¹¹ kg / m³

Answer : B

Question. The function of heavy water in a nuclear reactor to
(a) slow down the neutrons
(b) increase the neutrons
(c) stop the electrons
(d) none of these

Answer : A

Question. Which one of the following has the highest neutrons ratio ?
(a) ₉₂U²³⁵
(b) ₈O¹⁶
(c) ₂He⁴
(d) ₂₆Fe⁵⁶

Answer : A

Question. When radioactive substance emits an a-particle, then its position in the periodic table is lowered by
(a) two places
(b) three places
(c) five places
(c) one place

Answer : A

Question. 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

Answer : C

Question. Atomic weight of Boron is 10.81 and it has two isotopes ₅B¹⁰ and ₅B¹¹. Then the ratio of ₅B¹⁰ : ₅B¹¹ in nature would be
(a) 15 : 16
(b) 10 : 11
(c) 19 : 81
(d) 81 : 19

Answer : C

Question. Carbon dating is best suited for determining the age of fossils if their age in years is of the order of
(a) 10³
(b) 10⁴
(c) 10⁵
(d) 10⁶

Answer : B

Question. When an electron-positron pair annihilates, the energy released is about
(a) 0.8 × 10^–13 J
(b) 1.6 × 10^–13 J
(c) 3.2 × 10^–13 J
(d) 4.8 × 10^–13 J

Answer : B

Question. Carbon dating is best suited for determining the age of fossils if their age in years is of the order of
(a) 10³
(b) 10⁴
(c) 10⁵
(d) 10⁶

Answer : B

Question. When an electron-positron pair annihilates, the energy released is about
(a) 0.8 × 10^–13 J
(b) 1.6 × 10^–13 J
(c) 3.2 × 10^–13 J
(d) 4.8 × 10^–13 J

Answer : B