Chapter 13: Nuclei Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): The nuclear density is independent of the mass number A. Reason (R): The nuclear radius R is proportional to A^(1/3), so the nuclear volume is proportional to A.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Isotopes of the same element have identical chemical properties. Reason (R): Isotopes have the same number of protons and hence the same electronic configuration.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): The binding energy per nucleon is maximum for iron (A = 56). Reason (R): Iron is the most radioactive element found in nature.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 4

Logic Check

Assertion (A): Nuclear fission of uranium releases much more energy per kilogram than burning coal. Reason (R): The energy changes in nuclear reactions involve MeV per event, while chemical reactions involve only eV per event.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): A free neutron is unstable and decays with a mean life of about 1000 seconds. Reason (R): Inside the nucleus, the neutron is also unstable and continuously decays.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 6

Logic Check

Assertion (A): Nuclear fusion reactions require very high temperatures. Reason (R): At high temperatures, nuclei have sufficient kinetic energy to overcome the Coulomb potential barrier and come within the range of nuclear forces.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): In gamma decay, both atomic number Z and mass number A of the nucleus remain unchanged. Reason (R): Gamma rays are high-energy electromagnetic photons with no charge or mass.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): Binding energy per nucleon is nearly constant for nuclei with mass number 30 < A < 170. Reason (R): Nuclear force is long-range, so all nucleons in a large nucleus interact with each other.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): The mass of a nucleus is always less than the sum of the masses of its constituent protons and neutrons. Reason (R): When nucleons bind together, energy is released, and by E = mc², this corresponds to a decrease in mass (mass defect).

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Elements heavier than iron cannot be synthesized by fusion in stellar interiors. Reason (R): Fusion of nuclei heavier than iron would be endothermic, as these nuclei lie beyond the peak of the binding energy per nucleon curve.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 11

Logic Check

Assertion (A): The nuclear force between a proton-proton pair is the same as between a neutron-neutron pair. Reason (R): Nuclear force is charge-independent.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 12

Logic Check

Assertion (A): Tritium (³₁H) does not occur naturally in significant quantities. Reason (R): Tritium nuclei are unstable and undergo radioactive decay.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): In a nuclear reaction, the number of atoms of each element is conserved on both sides of the equation. Reason (R): In nuclear reactions, elements may transmute, so the number of atoms of each element need not be conserved.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): Radioactivity is a nuclear phenomenon unaffected by temperature, pressure, or chemical environment. Reason (R): The radioactive decay originates from the nucleus, which is shielded from external physical and chemical conditions by the electron cloud.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 15

Logic Check

Assertion (A): Atom bomb works on the principle of uncontrolled nuclear fission chain reaction. Reason (R): In each fission event, 2–3 neutrons are released which can trigger further fission reactions.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): In beta-minus decay, the mass number A of the nucleus remains the same. Reason (R): A beta-minus particle (electron) has negligible mass and in beta-minus decay a neutron converts to a proton, keeping A unchanged.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 17

Logic Check

Assertion (A): The gravitational force plays no significant role in nuclear binding. Reason (R): The gravitational force between nucleons is many orders of magnitude weaker than both the nuclear force and the Coulomb force.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): Energy is released when lighter nuclei fuse to form a heavier nucleus. Reason (R): The heavier nucleus formed in fusion has a lower binding energy per nucleon than the lighter nuclei.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): The proton-proton cycle in the sun converts four hydrogen nuclei into one helium-4 nucleus. Reason (R): The mass of four hydrogen nuclei is greater than the mass of one helium-4 nucleus, and this mass difference is released as energy.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 20

Logic Check

Assertion (A): The activity of a radioactive sample decreases exponentially with time. Reason (R): The rate of decay is proportional to the number of undecayed nuclei present at that time.

Reasoning Options

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Chapter sections

Chapter 13: Nuclei | Assertion-Reason

Assertion (A): The nuclear density is independent of the mass number A. Reason (R): The nuclear radius R is proportional to A^(1/3), so the nuclear volume is proportional to A.

Assertion (A): Isotopes of the same element have identical chemical properties. Reason (R): Isotopes have the same number of protons and hence the same electronic configuration.

Assertion (A): The binding energy per nucleon is maximum for iron (A = 56). Reason (R): Iron is the most radioactive element found in nature.

Assertion (A): Nuclear fission of uranium releases much more energy per kilogram than burning coal. Reason (R): The energy changes in nuclear reactions involve MeV per event, while chemical reactions involve only eV per event.

Assertion (A): A free neutron is unstable and decays with a mean life of about 1000 seconds. Reason (R): Inside the nucleus, the neutron is also unstable and continuously decays.

Assertion (A): Nuclear fusion reactions require very high temperatures. Reason (R): At high temperatures, nuclei have sufficient kinetic energy to overcome the Coulomb potential barrier and come within the range of nuclear forces.

Assertion (A): In gamma decay, both atomic number Z and mass number A of the nucleus remain unchanged. Reason (R): Gamma rays are high-energy electromagnetic photons with no charge or mass.

Assertion (A): Binding energy per nucleon is nearly constant for nuclei with mass number 30 < A < 170. Reason (R): Nuclear force is long-range, so all nucleons in a large nucleus interact with each other.

Assertion (A): The mass of a nucleus is always less than the sum of the masses of its constituent protons and neutrons. Reason (R): When nucleons bind together, energy is released, and by E = mc², this corresponds to a decrease in mass (mass defect).

Assertion (A): Elements heavier than iron cannot be synthesized by fusion in stellar interiors. Reason (R): Fusion of nuclei heavier than iron would be endothermic, as these nuclei lie beyond the peak of the binding energy per nucleon curve.

Assertion (A): The nuclear force between a proton-proton pair is the same as between a neutron-neutron pair. Reason (R): Nuclear force is charge-independent.

Assertion (A): Tritium (³₁H) does not occur naturally in significant quantities. Reason (R): Tritium nuclei are unstable and undergo radioactive decay.

Assertion (A): In a nuclear reaction, the number of atoms of each element is conserved on both sides of the equation. Reason (R): In nuclear reactions, elements may transmute, so the number of atoms of each element need not be conserved.

Assertion (A): Radioactivity is a nuclear phenomenon unaffected by temperature, pressure, or chemical environment. Reason (R): The radioactive decay originates from the nucleus, which is shielded from external physical and chemical conditions by the electron cloud.

Assertion (A): Atom bomb works on the principle of uncontrolled nuclear fission chain reaction. Reason (R): In each fission event, 2–3 neutrons are released which can trigger further fission reactions.

Assertion (A): In beta-minus decay, the mass number A of the nucleus remains the same. Reason (R): A beta-minus particle (electron) has negligible mass and in beta-minus decay a neutron converts to a proton, keeping A unchanged.

Assertion (A): The gravitational force plays no significant role in nuclear binding. Reason (R): The gravitational force between nucleons is many orders of magnitude weaker than both the nuclear force and the Coulomb force.

Assertion (A): Energy is released when lighter nuclei fuse to form a heavier nucleus. Reason (R): The heavier nucleus formed in fusion has a lower binding energy per nucleon than the lighter nuclei.

Assertion (A): The proton-proton cycle in the sun converts four hydrogen nuclei into one helium-4 nucleus. Reason (R): The mass of four hydrogen nuclei is greater than the mass of one helium-4 nucleus, and this mass difference is released as energy.

Assertion (A): The activity of a radioactive sample decreases exponentially with time. Reason (R): The rate of decay is proportional to the number of undecayed nuclei present at that time.

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