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:

Never confuse the "strong nuclear force" (which binds the nucleus together) with the "weak nuclear force" (which mediates radioactive decay).
Also, remember the strong force's repulsive core property; it is the reason nuclei maintain a relatively constant density.

Answer 1

The Correct Option is D

Concept:
• The strong nuclear force is the fundamental interaction responsible for binding nucleons (protons and neutrons) tightly together to form atomic nuclei.

• It is the strongest of the four fundamental forces in nature, vastly overpowering electrostatic repulsion between protons at short distances.

• However, its behavior is highly distance-dependent. It is strongly attractive between distances of roughly 0.7 fm and 2.5 fm.

• Crucially, at distances less than approximately 0.7 fm, the strong nuclear force becomes fiercely repulsive. This is known as the "repulsive core" and prevents the nucleus from collapsing in on itself.

Step 1: Evaluate the Assertion (A)
Assertion (A) states: "Nuclear forces are always attractive."
Based on the physical characteristics described in the concepts, this statement is factually incorrect.
While it is primarily attractive to hold the nucleus together, it possesses a critical repulsive core at extremely short internucleon distances (less than 0.7 femtometers).
If the force were exclusively and always attractive, nucleons would crush together infinitely.
Therefore, Assertion (A) is definitively False.

Step 2: Evaluate the Reason (R)
Reason (R) states: "The nuclear force between protons and neutrons in a nucleus is a weak force."
There are four distinct fundamental forces: Gravity, Electromagnetism, Weak Nuclear, and Strong Nuclear.
The force responsible for holding protons and neutrons together in a nucleus is specifically the strong nuclear force.
The "weak force" (or weak interaction) is an entirely different fundamental force responsible for phenomena like radioactive beta decay.
Describing the primary binding force of the nucleus as a "weak force" is completely scientifically inaccurate.
Therefore, Reason (R) is also definitively False.

Step 3: Conclusion
Since both the Assertion (A) and the Reason (R) contain factually incorrect statements regarding nuclear physics, the correct choice is (D).