Assertion (A): place of thymine. In RNA uracil is present at the place of thymine.
Reason (R): 5-methyl uracil is chemical name of thymine.

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.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "in RNA, uracil is present at the place of thymine."
- In DNA, the nitrogenous bases include adenine (A), thymine (T), cytosine (C), and guanine (G).
- In RNA, thymine (T) is replaced by uracil (U). Therefore, the bases in RNA are adenine (A), uracil (U), cytosine (C), and guanine (G).
- This statement is **true**.

2. **Understanding the Reason (R)**:
- The reason states that "5-methyl uracil is the chemical name of thymine."
- Thymine is indeed chemically known as 5-methyluracil because it has a methyl group (–CH3) attached to the 5th carbon of the uracil structure.
- This statement is also **true**.

3. **Analyzing the Relationship**:
- While both the assertion and the reason are true, we need to determine if the reason is the correct explanation for the assertion.
- The assertion explains a structural difference between DNA and RNA, while the reason provides a chemical name for thymine but does not explain why uracil is used in RNA instead of thymine.
- Therefore, the reason does not adequately explain the assertion.

4. **Conclusion**:
- Both the assertion and the reason are true, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Both assertion and reason are true; however, the reason is not the correct explanation for the assertion.

---