Assertion : A larger dry cell has higher emf.
Reason : The emf of a dry cell is proportional to its size.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are truw but reason is not correct explanation of assertion
C. If assertion is true but reason is false
D. If both assertion and reason are false.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states, "A larger dry cell has higher EMF."
- This implies that the size of the dry cell directly correlates with its electromotive force (EMF).

2. **Analyzing the Reason**:
- The reason states, "The EMF of a dry cell is proportional to its size."
- This suggests that as the size of the dry cell increases, the EMF also increases proportionally.

3. **Evaluating the Assertion**:
- In reality, the EMF of a dry cell is determined by the chemical reactions occurring within the cell, specifically the types of materials used for the electrodes and the electrolyte, not by the physical size of the cell.
- Therefore, the assertion that a larger dry cell has higher EMF is **false**.

4. **Evaluating the Reason**:
- Since the EMF is not dependent on the size of the cell but rather on the chemical properties and reactions, the reason that the EMF of a dry cell is proportional to its size is also **false**.

5. **Conclusion**:
- Both the assertion and the reason are false. Hence, the correct answer is that both statements are incorrect.

### Final Answer:
- **Assertion**: False
- **Reason**: False
- Therefore, the correct option is D (Both assertion and reason are false).