Assertion: No real body is truly rigid.
Reason: A rigid body is a body with a perfectly definite and unchanging shape. The distances between different pairs of particles of such a body do not change.

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.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states: "No real body is truly rigid."
- A rigid body is defined as one that does not undergo deformation when forces are applied. However, in reality, all materials will deform to some extent when subjected to enough force, even if the deformation is negligible. Therefore, the assertion is correct.

### Step 2: Understand the Reason
The reason states: "A rigid body is a body with a perfectly definite and unchanging shape. The distances between different pairs of particles of such a body do not change."
- This definition aligns with the concept of a rigid body in physics. A rigid body maintains its shape and the distances between particles remain constant under the application of forces. This also supports the assertion that no real body can be truly rigid, as real materials will always experience some deformation.

### Step 3: Conclusion
Both the assertion and the reason are correct. The reason provides a valid explanation for the assertion. Thus, we can conclude that:
- The assertion is true: No real body is truly rigid.
- The reason is true and correctly explains the assertion.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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