Note: In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
Assertion : Alkanes having more than three carbon atoms exhibit chain isomerism.
Reason : All carbon atoms in alkanes are `sp^3` hybridized.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that "Alkanes having more than three carbon atoms exhibit chain isomerism." This means that alkanes with four or more carbon atoms can exist in different structural forms (isomers) due to variations in the arrangement of the carbon chain.

2. **Analyzing the Reason**: The reason provided is "All carbon atoms in alkanes are sp³ hybridized." This indicates that each carbon atom in alkanes forms four single bonds (due to sp³ hybridization), which is characteristic of alkanes.

3. **Evaluating the Assertion**: To verify the assertion, we can consider alkanes with more than three carbon atoms. For example, butane (C₄H₁₀) has two structural isomers: n-butane and isobutane. This confirms that alkanes with more than three carbon atoms do exhibit chain isomerism.

4. **Evaluating the Reason**: The reason states that all carbon atoms in alkanes are sp³ hybridized. This is indeed true for alkanes, as they consist of single bonds only. However, while this fact is true, it does not directly explain why alkanes with more than three carbon atoms exhibit chain isomerism.

5. **Conclusion**: Since both the assertion and reason are true, but the reason does not correctly explain the assertion, we conclude that the correct answer is option B: "If both assertion and reason are true, but the reason is not the correct explanation of the assertion."