A: During gel electrophoresis, the DNA fragments move towards the anode.
R: DNA fragments are negatively charged molecules .

Options

A. If both Assertion and Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion and Reason are true but the reason is not the correct explanation of the assertion then mark (2).
C. If Assertion is true but Reason are false, then mark(3).
D. If both Assertion and Reason are false, then mark(4).

Answer

### Step-by-Step Text Solution:

1. **Understanding the Assertion**: The assertion states that during gel electrophoresis, DNA fragments move towards the anode. This is a fundamental principle of gel electrophoresis, which is a technique used to separate DNA fragments based on size.

2. **Understanding the Reason**: The reason provided is that DNA fragments are negatively charged molecules. This is true because the phosphate backbone of DNA carries a negative charge due to the presence of phosphate groups.

3. **Connecting Assertion and Reason**: Since DNA is negatively charged, when an electric field is applied during gel electrophoresis, the negatively charged DNA fragments will migrate towards the positively charged electrode, known as the anode.

4. **Conclusion**: Both the assertion and the reason are correct. The assertion correctly describes the movement of DNA fragments during gel electrophoresis, and the reason correctly explains why this movement occurs.

5. **Final Answer**: Therefore, the correct option is that both the assertion and the reason are true, and the reason is a correct explanation of the assertion.