A : potentiometer can act as an ideal voltmeter .
R : An idea, voltmeter has infinite resistance .

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion , then mark
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion then mark.
C. If Assertion is ture statement but Reason is false , then mark
D. If both Assertion and Reason are false statements then mark.

Answer

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

**Assertion (A): A potentiometer can act as an ideal voltmeter.**
**Reason (R): An ideal voltmeter has infinite resistance.**

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- A potentiometer is a device used to measure the potential difference (voltage) across two points in a circuit without drawing any current from the circuit. This characteristic allows it to provide an accurate voltage measurement, which is the defining feature of an ideal voltmeter.

**Hint**: Recall what a potentiometer does and how it measures voltage without affecting the circuit.

2. **Understanding the Reason**:
- An ideal voltmeter is defined as a voltmeter that has infinite resistance. This means that it does not allow any current to pass through it when connected across two points in a circuit. If no current flows, the voltmeter does not affect the circuit, ensuring that the voltage measured is the true voltage across the points.

**Hint**: Think about the implications of infinite resistance on current flow and measurement accuracy.

3. **Connecting the Assertion and Reason**:
- Since a potentiometer does not draw any current while measuring voltage (the current through it is zero), it behaves like an ideal voltmeter. The reason provided supports the assertion because the infinite resistance of an ideal voltmeter ensures that it does not draw current, which is a characteristic of the potentiometer.

**Hint**: Consider how the properties of an ideal voltmeter relate to the operation of a potentiometer.

4. **Evaluating the Correctness**:
- Both the assertion (A) and the reason (R) are correct statements. However, the reason does not fully explain why the assertion is true. While it provides a necessary condition (infinite resistance), it does not explain the operational mechanism of how the potentiometer achieves this.

**Hint**: Reflect on the relationship between the assertion and reason—are they directly linked or just related concepts?

5. **Conclusion**:
- Since both statements are correct but the reason does not adequately explain the assertion, the answer to the question is that both A and R are correct, but R is not the correct explanation for A.

### Final Answer:
Both A and R are correct, but R is not the correct explanation for A.