Assertion: Puberty is the age at which an individual becomes sexually mature.
Reason: In girls, puberty occurs at younger age than boys.

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.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Puberty is the age at which an individual becomes sexually mature." This is a true statement because puberty marks the developmental stage where an individual develops the physical and hormonal changes necessary for sexual reproduction.

2. **Understanding the Reason**: The reason given is "In girls, puberty occurs at a younger age than boys." This statement is also true. Generally, girls begin puberty earlier than boys, typically around ages 10-14 for girls and 12-16 for boys.

3. **Evaluating the Relationship**: Now we need to evaluate whether the reason provided is the correct explanation for the assertion. While both statements are true, the reason does not explain why puberty is the age of sexual maturity. The assertion is about the definition of puberty, while the reason merely states a fact about the timing of puberty in different genders.

4. **Conclusion**: Since both the assertion and the reason are true, but the reason does not correctly explain the assertion, the correct answer is that both statements are true but the reason is not the correct explanation of the assertion.

5. **Final Answer**: Therefore, the correct option is **Option B**: Both are true, but the reason is not the correct reason for the assertion.