A : If net force acting-on a system is zero, then work done on the system may be nonzero.
R : Internal forces acting on a system can increase its kinetic energy.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are falsė statements, then mark (4).

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided in the statement.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that if the net force acting on a system is zero, then the work done on the system may be non-zero.
- In physics, if the net external force on a system is zero, it means that the system is in a state of equilibrium. However, this does not necessarily mean that the internal forces cannot do work.

**Hint**: Think about systems where internal forces can cause changes, like explosions or collisions.

2. **Example of Internal Forces Doing Work**:
- Consider a bomb that explodes. Before the explosion, the net external force on the bomb is zero. However, when it explodes, the internal forces (due to the chemical energy stored in the bomb) cause the fragments to move apart with kinetic energy.
- This movement indicates that work has been done by the internal forces, even though the net external force was zero.

**Hint**: Recall examples of systems where internal energy is converted into kinetic energy.

3. **Understanding the Reason (R)**:
- The reason states that internal forces acting on a system can increase its kinetic energy.
- This is true because the internal forces, such as those during an explosion, convert potential energy (or internal energy) into kinetic energy, leading to an increase in the kinetic energy of the system's particles.

**Hint**: Consider how energy transformations occur within a system.

4. **Conclusion**:
- Both the assertion (A) and the reason (R) are correct. The assertion is supported by the example of the bomb explosion, and the reason explains how internal forces contribute to changes in kinetic energy.
- Therefore, the final answer is that both A and R are correct, and R is the correct explanation for A.

**Hint**: Always check if the reason logically supports the assertion.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and R is the correct explanation for A.