A : Gravitational potential is constant everywhere inside a spherical shell .
R : Gravitational field inside a spherical shell is zero everywhere .

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 Assertion is false statement but Reason is true , then mark (4)

Answer

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

**Assertion (A):** Gravitational potential is constant everywhere inside a spherical shell.

**Reason (R):** Gravitational field inside a spherical shell is zero everywhere.

### Step-by-Step Solution:

1. **Understanding the Gravitational Field Inside a Spherical Shell:**
- According to the shell theorem, the gravitational field inside a uniform spherical shell of mass is zero at every point. This means that if you are inside the shell, the gravitational forces exerted by the mass of the shell cancel each other out completely.

2. **Implication of Zero Gravitational Field:**
- The gravitational field (E) is related to the gravitational potential (V) by the equation:
\[ E = -\frac{dV}{dr} \]
- If the gravitational field E is zero, then the derivative of the potential with respect to distance (dr) is also zero. This implies that the gravitational potential does not change with distance inside the shell.

3. **Conclusion About Gravitational Potential:**
- Since the gravitational field is zero, the gravitational potential must be constant throughout the interior of the spherical shell. Thus, we can conclude that the assertion (A) is true.

4. **Analyzing the Reason:**
- The reason (R) states that the gravitational field inside the spherical shell is zero everywhere, which we have established to be true based on the shell theorem.

5. **Connecting Assertion and Reason:**
- Since both the assertion (A) and the reason (R) are true, and the reason correctly explains why the assertion is true, we conclude that the answer to the question is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

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