Assertion A potentiometer is preferred over that of a voltmeter for measurement of emf of a cell
Reason potentiometer does not draw any current from the cell.

Options

A. Both assertin and reason are true and reason is the correct explanation of assertion
B. Both assertion and reason are true but reason is not the correct explanation of assertion
C. Assertion is true but reason is flase
D. Both assertion and reason are false

Explanation

To solve the question, we need to analyze the assertion and reason provided:

**Assertion:** A potentiometer is preferred over that of a voltmeter for measurement of emf of a cell.

**Reason:** A potentiometer does not draw any current from the cell.

### Step-by-Step Solution:

1. **Understanding the Potentiometer:**
- A potentiometer is an instrument used to measure the electromotive force (emf) of a cell by balancing it against a known voltage. It operates on the principle of null deflection, meaning it measures voltage without drawing current from the source.

2. **Understanding the Voltmeter:**
- A voltmeter is an instrument that measures the potential difference (voltage) across two points in a circuit. When connected to a cell, it draws some current from the cell, which can affect the measurement.

3. **Current Drawn by the Voltmeter:**
- When a voltmeter is connected across a cell, it has a finite resistance. This resistance allows current to flow through the voltmeter, which can lead to a voltage drop across the internal resistance of the cell. As a result, the reading on the voltmeter may be less than the actual emf of the cell.

4. **Current Drawn by the Potentiometer:**
- In contrast, a potentiometer has a very high resistance (ideally infinite). When connected to a cell, it does not draw any significant current. Therefore, the entire current from the cell flows through the rest of the circuit, and the potentiometer measures the emf accurately without any voltage drop.

5. **Conclusion:**
- Since the potentiometer does not draw current from the cell, it provides a more accurate measurement of the emf compared to a voltmeter. Thus, the assertion is true, and the reason provided is also true and correctly explains why the assertion holds.

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