Assertion : Untranslated regions are sequences of RNA before initiation codon and after termination codon.
Reason : Untranslated regions provide stability to mRNA and also increase translational efficiency.

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

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
The assertion states that untranslated regions (UTRs) are sequences of RNA located before the initiation codon (AUG) and after the termination codon.
- **Explanation**: In mRNA, the UTRs are segments that do not code for proteins. The 5' UTR is located upstream of the start codon, and the 3' UTR is located downstream of the stop codon.

2. **Evaluating the Reason**:
The reason provided states that untranslated regions provide stability to mRNA and also increase translational efficiency.
- **Explanation**: UTRs play a crucial role in the stability of mRNA molecules, protecting them from degradation. They also contain regulatory elements that can enhance the efficiency of translation.

3. **Determining the Truth of the Assertion**:
Since UTRs are indeed located before the initiation codon and after the termination codon, the assertion is true.

4. **Determining the Truth of the Reason**:
The reason is also true because UTRs do provide stability to mRNA and enhance translational efficiency.

5. **Analyzing the Relationship Between Assertion and Reason**:
Although both the assertion and reason are true, the reason does not directly explain why the assertion is true. The assertion describes the location of UTRs, while the reason discusses their function.

6. **Conclusion**:
Based on the evaluation, both the assertion and reason are true, but the reason does not serve as a correct explanation for the assertion. Therefore, the correct answer is option B: "Both assertion and reason are true, but reason is not the correct explanation for assertion."