Assertion : In case of potentiometer experiment, if emfs of known and unknown both batteries are increased two times, then null point length will remain unchanged.
Reason : Null point length does not depend on emf of either of the two batteries.

Options

A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true and Reason is not correct explanation of Assertion.
C. If Assertion is true but Reason is false.
D. If Assertion is false but Reason is true.

Answer

To solve the given question, we will analyze the assertion and the reason provided in the context of the potentiometer experiment.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
The assertion states that if the EMFs of both the known and unknown batteries are increased two times, then the null point length will remain unchanged.

2. **Understanding the Potentiometer Principle**:
A potentiometer measures the potential difference (voltage) across a component by balancing it against a known voltage. The null point is the point along the wire where the potential difference is equal to the EMF of the unknown battery.

3. **Effect of Increasing EMF**:
When both the known and unknown EMFs are increased to two times their original values, the potential difference across the potentiometer wire will also increase proportionally. However, since both EMFs are increased equally, the ratio of their effects on the null point remains the same.

4. **Mathematical Representation**:
The potential drop across the potentiometer wire is given by:
\[ V = \frac{E_1 \cdot R}{R + r} \]
where \(E_1\) is the EMF of the known battery, \(R\) is the resistance of the potentiometer wire, and \(r\) is the internal resistance of the known battery.

5. **Null Point Length**:
The null point length \(L\) is directly proportional to the EMF of the battery being measured. If both EMFs are doubled, the potential drop across the potentiometer wire will also double, but since both sides of the equation are affected equally, the null point remains at the same length.

6. **Conclusion on Assertion**:
Therefore, the assertion is **true**: the null point length will remain unchanged when both EMFs are increased two times.

7. **Understanding the Reason**:
The reason states that the null point length does not depend on the EMF of either of the two batteries. This statement is **false** because the null point length is indeed dependent on the EMF of the known battery.

8. **Final Evaluation**:
Since the assertion is true and the reason is false, the correct conclusion is that the assertion is correct, but the reason is incorrect.

### Final Answer:
- Assertion: True
- Reason: False