A : parctically a voltmeter will measure the voltage across the battery but not its EMF.
R : EMF of a cell is measured with the help of a potentiometer .

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 both statements A and R and determine their correctness and relationship.

### Step-by-Step Solution:

1. **Understanding Statement A**:
- Statement A claims that a voltmeter measures the voltage across the battery but not its EMF.
- A voltmeter is designed to measure the potential difference (voltage) between two points in a circuit. When connected across a battery, it measures the voltage drop across the battery terminals, which can be affected by the internal resistance of the battery and the current flowing through it.
- Therefore, the voltmeter measures the terminal voltage (V), which is given by the equation:
\[ V = E - I \cdot r \]
where \( E \) is the EMF of the battery, \( I \) is the current, and \( r \) is the internal resistance.
- Thus, Statement A is **correct**.

2. **Understanding Statement R**:
- Statement R states that the EMF of a cell is measured with the help of a potentiometer.
- A potentiometer is an instrument used to measure the EMF of a cell accurately. It works on the principle of null deflection, meaning it measures the potential difference without drawing any current from the cell.
- When the current is zero, the voltage measured across the potentiometer wire corresponds to the EMF of the cell. Thus, Statement R is also **correct**.

3. **Analyzing the Relationship**:
- Statement A and Statement R are both correct, but they address different aspects of electrical measurement.
- Statement A discusses the limitations of a voltmeter in measuring EMF due to the presence of internal resistance and current, while Statement R explains how EMF can be accurately measured using a potentiometer.

4. **Conclusion**:
- Since both statements are correct but do not provide a correct explanation for each other, the answer to the question is that both A and R are correct, but R is not a correct explanation for A.

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