NEET Physics Nuclei MCQs Set A

a) the containers will in general have different numbers of the atoms of the material but their average will be close to 5000

b) none of the containers can have more than 5000 atoms.

c) all the contains will conatin the same number of atoms of the material but that number will only be approximately 5000

d) All of these

Answer: the containers will in general have different numbers of the atoms of the material but their average will be close to 5000

Question: When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom

a)

b)

c)

d)

Answer:

Question: Heavy stable nuclei have more neutrons than protons. this is because of the fact that

a) electrostatic force between protons are repulsive

b) neutrons decay into protons through beta decay

c) nuclear force between neutrons are weaker than that between protons

d) neutrons are heavier than protons

Answer: electrostatic force between protons are repulsive

Question: In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. the moderator used have light nuclei. Heavy nuclei will not serve the purpose, because

a) elastic collision of neutrons with heavy nuclei will not slow them down

b) the net weight of the reactor would be unbearably high

c) substances with heavy nuclei do not occur in liquid or gaseous state at room temperature

d) they will break up

Answer: elastic collision of neutrons with heavy nuclei will not slow them down

Question: A radio isotope ‘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) 4.20 × 10⁹ years

b) 1.96 × 10⁹ years

c) 8.40 × 10⁹ years

d) None of these

Answer:  4.20 × 10⁹ years

Question: A nucleus of uranium decays at rest into nuclei of thorium and helium. Then

a) the helium nucleus has more kinetic energy than the thorium nucleus

b) the helium nucleus has less kinetic energy than the thorium nucleus.

c) the helium nucleus has less momentum than the thorium nucleus.

d) the helium nucleus has more momentum than the thorium nucleus.

Answer: the helium nucleus has more kinetic energy than the thorium nucleus

Question: Assertion : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion and
Reason : For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei it decreases with increasing Z.

a) If Assertion is correct but Reason is incorrect

b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.

c) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.

d) If both the Assertion and Reason are incorrect

Answer:  If Assertion is correct but Reason is incorrect

Question:  Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes, respectively. Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed number of A and B nuclei will be

a) 5 : 4

b) 1 : 16

c) 4 : 1

d) 1 : 4

Answer: 5 : 4

Question: 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) between 4 and 6

b) 2

c) 4

d) 6

Answer: between 4 and 6

Question: Assertion : Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion and
Reason : For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei it decreases with increasing Z.

a) If both the Assertion and Reason are incorrect

b) If Assertion is correct but Reason is incorrect

c) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion

d) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Answer:  If both the Assertion and Reason are incorrect

More Questions.....................................

Question:  A radioactive nucleus A with a half life T, decays into a nucleus B. At t = 0, there is no nucleus B. At sometime t, the ratio of the number of B to that of A is 0.3. Then, t is given by

a)

b)

c)

d)

Answer:

Question:  After two hours, one-sixteenth of the starting amount of a certain radioactive isotope remained undecayed. The half life of the isotope is

a) 30 minutes

b) 4 hour

c) 15 minutes

d) 45 minutes

Answer: 30 minutes

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) 15

d) 30

Answer: 20

Question: A radioactive substance with decay constant of 0.5s^–1 is being produced at a constant rate of 50 nuclei per second. If there are no nuclei present initially, the time (in second) after which 25 nuclei will be present is [

a) 2 ln (4/3)

b) ln (4/3)

c) ln 2

d) 1

Answer:  2 ln (4/3)