NEET Physics Chapter Wise Mock Test – Radioactivity

NEET Physics Chapter Wise Mock Test – Radioactivity

Question 1.
The activity of a radioactive sample is measured as 9750 counts/min at t = 0 and as 975 counts/min at t = 5 min. The decay constant is approximately
(a) 0.922/min
(b) 0.691/min
(c) 0.461/min
(d) 0.230/min

Question 2.
Samples of two radioactive nuclides A and B are taken. X_A and X_B are the disintegration constants of A and B, respectively. In which of the following cases, the two samples can simultaneously have the same decay rate at any time?
(a) Initial rate of decay of A is twice the initial rate of decay of 6 and X_A = X_B
(b) Initial rate of decay of A is twice the initial rate of decay of 6 and X_A > X_B
(c) Initial rate of decay of 6 is twice the initial rate of decay of A and X_A > X_B
(d) Initial rate of decay of B is always same

Question 3.
If a radioactive substance decays for time interval equal to its mean life, then the fraction of the substance remaining undecayed, will be
(a) 1/e
(b) 1/e²
(c) e²
(d) e

Question 4.
The variation of decay rate of two radioactive samples A and B with time is shown in figure.

Which of the following statements is/are true?
(a) Decay constant of A is greater than that of B, hence A always decays faster than B
(b) Decay constant of B is greater than that of A but its decay rate is always smaller than that of A
(c) Decay constant of A is greater than that of B but it does not always decay faster than B
(d) Decay constant of B is same as that of A but still its decay rate becomes equal to that of A at a later instant

Question 5.
Two Cu⁶⁴ nuclei touch each other. The electrostatic repulsive energy of the system will be
(a) 0.788 MeV
(b) 7.88 MeV
(c) 126.15 MeV
(d) 788 MeV

Question 6.
The graph of log(R/R₀) versus A (R=radius of a nucleus and A=mass number) is
(a) a circle
(b) an ellipse
(c) a parabola
(d) a straight line

Question 7.
Which stable nucleus has radius one third of that of Os¹⁸⁹?
(a) Be⁹
(b) Li⁷
(c) F¹⁹
(d) None of these

Question 8.
If the nuclear radius of ²⁷Al is 3.6 fm, the approximate nuclear radius of ²⁷Cu in Fermi is
(a) 2.4
(b) 1.2
(c) 4.8
(d) 3.6

Question 9.
The half-life of a radioactive material is 3h. If the initial amount is 300g, then after 18h, it will remain
(a) 4.68 g
(b) 46.8 g
(c) 9.375 g
(d) 93.75 g

Question 10.
The half-life of a radioactive isotope X is 50 yr. It decays to another element Y which is stable. The two elements X and Y were found to be in the ratio of 1:15 in a sample of a given rock. The age of the rock was estimated to be
(a) 200 yr
(b) 250 yr
(c) 100 yr
(d) 150 yr

Question 11.
A mixture consists of two radioactive materials A₁ and A₂ with half-lives of 20s and 10s, 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) 60s
(b) 80s
(c) 20s
(d) 40s

Question 12.
The half-life of radioactive element is 600 yr. The fraction of sample that would remain after 3000 yr, is
(a) 1/2
(b) 1/16
(c) 1/8
(d) 1/32

Question 13.
If 10% of a radioactive substance decays in every 5 yr, then the percentage of the substance that will have decayed in 20 yr, will be
(a) 40%
(b) 50%
(c) 65.6%
(d) 34.4%

Question 14.
A radioactive sample has an initial activity of 50 dpm, 20 min later, the activity is 25 dpm. How many atoms of the radioactive nuclide were there originally?
(a) 20
(b) 80
(c) 1443
(d) 5441

Question 15.
The activity of a radioactive sample is measured as Ne counts per minute at t=0 and N₀/e counts per minute at t=5 min. The time (in minute) at which the activity reduces to half its value, is
(a) log_e 2/5
(b) 5/log_e 2
(c) 5 log₁₀ 2
(d) 5log_e 2

Question 16.
Half-life of a radioactive substance is 20 min. The time between 20% and 80% decay will be
(a) 20 min
(b) 40 min
(c) 80 min
(d) 60 min

Question 17.

Question 18.
If mass of proton = 1.008 amu and mass of neutron = 1.009 amu, then the binding energy per nucleon for ₄Be⁹ (mass = 9.012 amu) will be
(a) 0.0672 MeV
(b) 0.672 MeV
(c) 6.72 MeV
(d) 67.2 MeV

Question 19.
The mass of ₁₈Ar⁴⁰ is 39.9480 amu. Its mass defect will be (given that, m_p = 1.0078 amu and m_n=1.0087 amu)
(a) 0.3694
(b) 0.3318
(c) 0.3480
(d) 0.3838

Question 20.
The binding energy of neutron in deuterium ₁H² will be (given that, m_p= 1.0078 amu, m_n= 1.0087 amu and m_d = 2.0141 amu)
(a) 2.2344 MeV
(b) 4.4688 MeV
(c) 1.1172 MeV
(d) 7.8 MeV

Question 21.

Question 22.

Question 23.
If the mass defect in a fusion process is 0.3%, then the energy released in the fusion of 1kg of material will be
(a) 2.7 x 10¹⁴ J
(b)2.7x 10^-14 J
(c)2.7x 10¹⁴ erg
(d)2.7x 10¹⁴ eV

Question 24.
The binding energy of deuteron is 2.2 MeV and that of ⁴₂He, is 28 MeV. If two deuterons are fused to form one ⁴₂He, then the energy released is
(a) 25.8 MeV
(b) 23.6 MeV
(c) 19.2 MeV
(d) 30.2 MeV

Question 25.
Heavy stable nuclei have more neutrons than protons. This is because of the fact, that
(a) neutrons are heavier than protons
(b) electrostatic force between protons is repulsive
(c) neutrons decay into protons through β-decay
(d) nuclear forces between neutrons is weaker than that between protons

Question 26.
If 200 MeV energy is obtained per fission of ₉₂U²³⁵, then the number of fissions per second to produce 1kW power will be
(a) 1.25×10¹⁸
(b) 3.2×10^-8
(c) 3.125×10¹³
(d) 0.125×10¹³

Question 27.
If all the atoms of 1kg of deuterium undergo nuclear fusion, then the amount of energy released will be
(a) 6×10²⁷ cal
(b) 2×10⁷ kWh
(c) 56.9×10¹³ J
(d) 8×10²³ MeV

Question 28.
On fission of one nucleus of U²³⁵, the amount of energy obtained is 200 MeV. The power obtained in a reactor is 1000 kW. Number of nuclei fissioned per second in the reactor, is
(a) 9.4×10¹⁶ s^-1
(b) 2.3×10⁸ s^-1
(c) 3.125×10¹⁶ s^-1
(d) 4.2×10⁸ s^-1

Question 29.
The mass of uranium required per day to generate 1MW power from the fission of ₉₂U²³⁵, will be
(a) 1.05g
(b) 2.05g
(c) 3.05g
(d) 4.05g

Question 30.
10¹⁴ fissions per second are taking place in a nuclear reactor having efficiency 40%. The energy released per fission is 250 MeV. The power output of the reactor is
(a) 2000 W
(b) 4000 W
(c) 1600 W
(d) 3200 W

Question 31.
An electron of 1.02 MeV and a positron of 1.02 MeV collide and annihilate into energy producing two γ-photons. The energy of each γ-photon will be
(a) 1.02 MeV
(b) 2.04 MeV
(c) 0.51 MeV
(d) 1.53 MeV

Question 32.
A nuclear explosive is designed to deliver 1 MW power in the form of heat energy. If the explosion is designed with a nuclear fuel consisting of U²³⁵ to run a reactor at this power level for one year, then the amount of fuel needed is (Given energy per fission is 200 MeV)
(a) 1 kg
(b) 0.01 kg
(c) 3.84 kg
(d) 0.384 kg

Question 33.
When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom
(a) do not change for any type of radioactivity
(b) change fora and β-radioactivity but not for γ-radioactivity
(c) change for α-radioactivity but not for others .
(d) change for β-radioactivity but not for others

Question 34.

Question 35.

Question 36.
A neutron causes fission in ₉₂U²³⁵ producing ₄₀Zr⁹⁷ and Te¹³⁴ and some neutrons. The atomic number of Te will be
(a) 50
(b) 51
(c) 52
(d) 53

Question 37.
A uranium reactor ₉₂U²³⁵ takes 30 days to use up 2 kg of fuel, each fission gives 185 MeV of usable energy, then power output is
(a) 32.23 MW
(b) 22.28 MW
(c) 58.46 MW
(d) None of these

Direction (Q.Nos. 38-42): In each of the following questions, a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
(a) If both Assertion and Reason are true and the Reason ‘ is the correct explanation of the Assertion
(b) If both Assertion and Reason are true but the Reason is not correct explanation of the Assertion
(c) If Assertion is true but Reason is false
(d) If both Assertion and Reason are false

Question 38.
Assertion(A): On α-decay, daughter nucleus shifts two places to the left from the parent nucleus.
Reason(R): An α-particle carries four units of mass.

Question 39.
Assertion (A): ⁹⁰Sr from the radioactive fall out from a nuclear bomb ends up in the bones of human beings through the milk consumed by them. It causes impairment of the production of red blood cells.
Reason (R): The energetic β-particles emitted in the decay of ⁹⁰Sr damage the bone marrow.

Question 40.

Question 41.
Assertion (A): the ratio of time taken for light emission from an atom to that for release of nuclear energy in fission is 1:100.
Reason (R): Time taken of the light emission from an atom is of the order of 10^-8 s.

Question 42.
Assertion (A): The mass of β-particles when they are emitted, is higher than the mass of electron obtained by other means.
Reason (R): β-particle and electron, both are similar particles.

Question 43.

Question 44.
A radio isotope X with a half life 1.4 x 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 x 10⁹ years
(b) 3.92 x 10⁹ years
(c) 4.20 x 10⁹ years
(d) 8.40 x 10⁹ years

Question 45.

Question 46.
The half-life of a radioactive isotope X is 20 yr. 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) 40yr
(b) 60yr
(c) 80yr
(d) 100yr

Question 47.
A certain mass of hydrogen is changed to helium by the process of fusion. The mass defect in fusion reaction is 0.02866u. The energy liberated per u, is (Given, 1u=931 MeV)
(a) 2.67 MeV
(b) 26.7 MeV
(c) 6.675 MeV
(d) 13.35 MeV

Question 48.
If the half-life of any sample of radioactive substance is 4 days, then the fraction of sample will remain undecayed after 2 days, will be
(a) √2
(b) 1/√2
(c) (√2-1)/√2
(d) 1/2

Question 49.
Consider the nuclear reaction X²⁰⁰ —–> A¹¹⁰+B⁸⁰. If the binding energy per nucleon for X, A and B are 7.4 MeV, 8.2 MeV and 8.1 MeV, respectively. Then, the energy released in the reaction is
(a) 70 MeV
(b) 200 MeV
(c) 190 MeV
(d) 10 MeV

Question 50.
Band spectrum is also called
(a) molecular spectrum
(b) atomic spectrum
(c) flash spectrum
(d) line absorption spectrum

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