Assertion (A): A primer is a small segment of DNA that binds to a complementary strand of DNA. Reason(R) : Primers are necessary to stop the functioning of DNA polymerase enzyme and, therefore, are necessary in polymerase chain reaction.

Options

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

Explanation

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided in the question.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states: "A primer is a small segment of DNA that binds to a complementary strand of DNA."
- **Analysis**: Primers are indeed short sequences of nucleotides that bind to the complementary DNA strand. However, it is important to note that in the context of the polymerase chain reaction (PCR), primers are typically short segments of RNA or DNA that initiate the synthesis of a new DNA strand. Therefore, while the assertion is partially correct, it is misleading because it does not specify that primers can be RNA or DNA.

2. **Understanding the Reason (R)**:
- The reason states: "Primers are necessary to stop the functioning of DNA polymerase enzyme and, therefore, are necessary in polymerase chain reaction."
- **Analysis**: This statement is incorrect. Primers do not stop the functioning of DNA polymerase; rather, they are essential for the initiation of DNA synthesis. DNA polymerase requires a primer with a free 3'-hydroxyl group to add nucleotides during DNA replication. Therefore, the reason provided is misleading and incorrect.

3. **Conclusion**:
- The assertion (A) is false because it does not accurately describe the nature of primers in PCR.
- The reason (R) is also false because it incorrectly states the role of primers in relation to DNA polymerase.
- Therefore, the correct answer is that both the assertion and the reason are false.

### Final Answer:
- Assertion (A) is false.
- Reason (R) is false.
- The answer is option 4: Both A and R are false.