Assertion: Centre of mass of a rigid body always lies inside the body.
Reason: Centre of mass and centre of gravity coincide if gravity is uniform.

Options

A. (a) If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.
B. (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
C. (c) If Assertion is true, but the Reason is false.
D. (d) If Assertion is false but the Reason is true.

Explanation

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

### Step 1: Analyze the Assertion
The assertion states that "the center of mass of a rigid body always lies inside the body."

- This statement is not universally true. For example, consider a hollow ring or a torus. The center of mass of a hollow ring is located at its geometric center, which is outside the material of the ring itself. Therefore, the assertion is false.

### Step 2: Analyze the Reason
The reason states that "the center of mass and center of gravity coincide if gravity is uniform."

- This statement is true. When gravity is uniform, the center of mass (the average position of all mass in the body) and the center of gravity (the point where the weight of the body can be considered to act) coincide. This is because the gravitational force acts uniformly on all parts of the body, leading to the same point for both concepts.

### Step 3: Conclusion
Based on the analysis:
- The assertion is false because the center of mass does not always lie inside the body (as shown with the example of a hollow ring).
- The reason is true because the center of mass and center of gravity coincide under uniform gravitational conditions.

Thus, the correct conclusion is that the assertion is false, and the reason is true.

### Final Answer
The correct option is D: Assertion is false but the reason is true.

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