CBSE Class 12 Physics Atoms and Nuclei Assignment Set A

Question. In Bohr’s theory, relation between principal quantum number n and radius of orbit r is:
(a) r ∝ 1/n²
(b) r ∝ n
(c) r ∝ 1/n
(d) r ∝ n2 

Answer :   D

Question. We wish to seen inside an atom. Assuming the atom to have a diameter of 100 pm, this means that one must be able to resolve a width of say 10 pm. If an electron microscope is used, the minimum electron energy required is about
(a) 1.5 keV
(b) 15 keV 
(c) 150 keV
(d) 1.5 MeV

Answer :   B

Question The ground state energy of hydrogen atom is – 13.6 eV. What is the potential energy of the electron in this state ? 
(a) 0 eV
(b) – 27.2 eV
(c) 1 eV
(d) 2 eV

Answer :   B

Important Questions for NCERT Class 12 Physics Nuclei 

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. 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. 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. 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. 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. The half life of radium is about 1600 years. If 100 g of radium existing now, 25 g will remain unchanged after
(a) 4800 years
(b) 6400 years
(c) 2400 years
(d) 3200 years 

Answer  :  D

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. A nuclear reaction given by ZXA → + Z+1Y^A + −1^e0 V^- represents
(a) b-decay
(b) g-decay
(c) fusion
(d) fission 

Answer  :  A

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

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. 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. 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. 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. 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. Actinium 231, 231Ac89, emit in succession two b-particles, four alphas, one b and one alpha plus several g rays. What is the resultant isotope:
(a) 221 Au79
(b) 211 Au 79 
(c) 221 Pb 82
(d) 211 Pb 82

Answer  D