A: If a clock based on simple pendulum is taken to hill it will become slower.
R: With increase of height above surface of earth g decreases so T will increase.

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 both Assertion and Reason are false statements, then mark (4)

Answer

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided:

**Assertion (A):** If a clock based on a simple pendulum is taken to a hill, it will become slower.

**Reason (R):** With an increase of height above the surface of the Earth, g decreases, so T will increase.

### Step-by-Step Solution:

1. **Understand the Assertion:**
- The assertion states that a clock based on a simple pendulum becomes slower when taken to a hill. This implies that the time it takes for the pendulum to complete one oscillation (the time period T) increases, leading to a slower clock.

2. **Understand the Reason:**
- The reason provided explains that as we go higher above the Earth's surface, the acceleration due to gravity (g) decreases. This is a true statement, as gravity decreases with altitude.

3. **Relate Time Period to Gravity:**
- The time period (T) of a simple pendulum is given by the formula:
\[ T = 2\pi \sqrt{\frac{L}{g}} \]
- Here, L is the length of the pendulum, and g is the acceleration due to gravity.

4. **Analyze the Effect of Decreasing g:**
- From the formula, we see that T is inversely proportional to the square root of g. If g decreases, T will increase:
\[ T \propto \frac{1}{\sqrt{g}} \]
- Therefore, as we move to a higher altitude (where g decreases), the time period T increases.

5. **Conclusion about the Assertion:**
- Since T increases, the clock will indeed become slower, which means the assertion (A) is true.

6. **Conclusion about the Reason:**
- The reason (R) is also true because it correctly states that g decreases with height.

7. **Final Evaluation:**
- Both the assertion and the reason are true, and the reason correctly explains the assertion.

### Final Answer:
Both assertion (A) and reason (R) are true, and R is the correct explanation for A.