Assertion: If net force on a system is zero, then momentum of every individual body remains constant.
Reason: If momentum of a system is constant, then kinetic energy of the system may change.

Options

A. If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are correct but Reason is not the correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If Assertion is false but Reason is true.

Explanation

To solve the question regarding the assertion and reason provided, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
The assertion states: "If net force on a system is zero, then momentum of every individual body remains constant."

- According to Newton's first law, if the net external force acting on a system is zero, the momentum of the entire system remains constant. However, this does not imply that the momentum of each individual body within the system remains constant. Individual bodies can still have momentum that changes as long as their changes balance out to keep the total momentum of the system constant.

**Conclusion for Assertion**: The assertion is **false**. The net force being zero means the total momentum of the system is constant, but individual momenta can change.

### Step 2: Analyze the Reason
The reason states: "If momentum of a system is constant, then kinetic energy of the system may change."

- The momentum of a system can be constant while the kinetic energy changes. This can occur in inelastic collisions, where momentum is conserved but kinetic energy is not. For example, two objects may collide and stick together, conserving momentum but losing some kinetic energy to sound, heat, or deformation.

**Conclusion for Reason**: The reason is **true**. Kinetic energy can change even when momentum is conserved.

### Final Conclusion
- The assertion is false, and the reason is true. Therefore, the correct answer is that the assertion is false, but the reason is true.