Assertion (A): Current should not be passed through potentiometer for a long time.
Reason (R): Lechanche cell should be used in main circuit of potentiometer.

Options

A. Both (A) and (R) are true and (R) is the correct explanation of (A).
B. Both (A) and (R) are true but (R) is not the correct explanation of (A).
C. (A) is true but (R) is false.
D. (A) is false and (R) is also false.

Explanation

To solve the question, we need to analyze both the Assertion (A) and the Reason (R) provided.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Current should not be passed through a potentiometer for a long time."
- This is true because if current flows through the potentiometer for an extended period, it can cause heating in the wire. This heating can affect the resistance of the wire and lead to inaccurate measurements.

2. **Understanding the Reason (R)**:
- The reason states that "Leclanché cell should be used in the main circuit of potentiometer."
- This statement is incorrect. A Leclanché cell is a type of primary cell, and while it can be used in circuits, it is not typically used as the main power source in a potentiometer. Instead, a potentiometer usually utilizes a secondary cell (like a rechargeable battery) for stable voltage.

3. **Evaluating the Relationship between A and R**:
- The assertion is true, while the reason is false. Therefore, the correct conclusion is that the assertion stands independently and is not supported by the reason.

4. **Final Conclusion**:
- The correct option is that Assertion (A) is true, and Reason (R) is false.