Question

Assertion (A) : Nuclear forces are always attractive.
Reason (R) : The nuclear force between protons and neutrons in a nucleus is a weak force.

• 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:

The nuclear force turns from attractive to repulsive at a critical threshold distance of \(r_0 \approx 0.8\text{ fm}\). This structural property ensures that individual nucleons maintain a stable, finite volume instead of collapsing together.

Answer 1

The Correct Option is D

Concept: The nuclear force is the strong binding interaction that holds protons and neutrons (nucleons) together inside an atomic nucleus. It has several distinct properties:
• Strength: It is the strongest known fundamental force in nature, roughly 100 times stronger than the electromagnetic force and \(10^{38}\) times stronger than gravitation at short distances.
• Distance Dependence: The nuclear force is short-ranged, operating effectively only over distances of a few femtometers (\(1\text{ fm} = 10^{-15}\text{ m}\)).
• Nature: The force is attractive at typical nucleon separations but becomes strongly repulsive at extremely short distances.

Step 1: Evaluating Assertion (A).
The Assertion states that nuclear forces are always attractive. However, the potential energy profile between two nucleons shows that the nuclear force depends strongly on the separation distance (\(r\)):
• For separations greater than the equilibrium distance (\(r > r_0 \approx 0.8\text{ fm}\)), the nuclear force is attractive, holding the nucleons together.
• For separations less than \(0.8\text{ fm}\), the potential energy rises sharply, and the nuclear force becomes strongly repulsive. This repulsion prevents the nucleus from collapsing into a single point. Since the nuclear force can be repulsive at very short distances, the statement that it is always attractive is false.

Step 2: Evaluating Reason (R).
The Reason states that the nuclear force between nucleons is a weak force. In physics, the "weak force" refers to the weak nuclear interaction responsible for radioactive decay processes (like beta decay). The force that binds nucleons together is the strong nuclear force, which is the strongest fundamental force in nature. Therefore, the Reason statement is completely false. Since both individual statements are false, this corresponds to Option (D).