Assertion : KE is conserved at every instant of elastic collision.
Reason : NO deformation of matter occurs in elastic collision.

Options

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

Answer

To solve the question regarding the assertion and reason related to elastic collisions, we will analyze both statements step by step.

### Step 1: Understanding Elastic Collision
An elastic collision is defined as a collision in which both momentum and kinetic energy are conserved.

### Step 2: Analyzing the Assertion
The assertion states that "KE is conserved at every instant of elastic collision."
- In an elastic collision, while the total kinetic energy before and after the collision is conserved, it is not conserved at every instant during the collision. During the collision, some kinetic energy is temporarily converted into potential energy due to deformation of the colliding bodies.

### Step 3: Analyzing the Reason
The reason states that "NO deformation of matter occurs in elastic collision."
- This statement is incorrect. In an elastic collision, there is indeed some deformation of the colliding objects. However, the key point is that the objects return to their original shape after the collision, and thus, the total kinetic energy can be restored.

### Step 4: Conclusion
Both the assertion and the reason are incorrect:
- The assertion is false because kinetic energy is not conserved at every instant.
- The reason is false because deformation does occur during the collision.

### Final Answer
Since both the assertion and the reason are false, the correct option is D: Both assertion and reason are false.

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