Question

Assertion (A) : The mass of a nucleus is less than the sum of the masses of the constituent nucleons. Reason (R) : Energy is absorbed when the nucleons are bound together to form a nucleus.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

Formation of a stable nucleus always releases energy. \[ \text{Mass defect} \Longleftrightarrow \text{Binding Energy} \] A larger binding energy means a more stable nucleus.

Answer 1

The Correct Option is C

The given assertion and reason statement deals with the concept of nuclear mass and binding energy in physics.

1. Understanding the Assertion:
   • The assertion states that the mass of a nucleus is less than the sum of the masses of the constituent nucleons (protons and neutrons).
   • This is a well-known fact in nuclear physics, often referred to as the mass defect.
   • When nucleons come together to form a nucleus, the total mass of the nucleus is actually less than the sum of the individual masses of the nucleons because some mass is converted into energy (binding energy) according to Einstein's mass-energy equivalence principle, E = mc^2.
   • The binding energy is the energy that holds the nucleons together within the nucleus.
2. Understanding the Reason:
   • The reason states that energy is absorbed when the nucleons are bound together.
   • However, this statement is incorrect. Rather than absorbing energy, energy is released when nucleons bind together to form a nucleus.
   • This release of energy is what makes the nucleus more stable and is described as the binding energy of the nucleus. Thus, the binding process is exothermic, meaning energy is released, not absorbed.
3. Conclusion:
   • Assertion (A) is true because of the mass defect explained by the conversion of mass to binding energy.
   • Reason (R) is false because binding nucleons release energy instead of absorbing it.
   • Hence, the correct answer is: Assertion (A) is true, but Reason (R) is false.