Assertion : Bakelite is formed when novalac is heated with formaldehyde and it is a thermosetting polymer.
Reason : Bakelite is an infusible solid mass

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 Bakelite is formed when novolac is heated with formaldehyde and that it is a thermosetting polymer.
- **Explanation**: Bakelite is indeed synthesized from novolac (a type of phenolic resin) when it is heated in the presence of formaldehyde. This process involves cross-linking of the polymer chains, which leads to the formation of a rigid structure.

2. **Identifying the Nature of Bakelite**: The assertion also claims that Bakelite is a thermosetting polymer.
- **Explanation**: Thermosetting polymers are characterized by their inability to be remolded or reshaped upon heating after they have been set. Once Bakelite is formed through the curing process, it cannot be melted or reshaped, which is a defining property of thermosetting polymers.

3. **Understanding the Reason**: The reason states that Bakelite is an infusible solid mass.
- **Explanation**: This statement is true. Bakelite, once formed, becomes an infusible solid mass due to the extensive cross-linking between the polymer chains. This cross-linking prevents the material from melting upon heating.

4. **Evaluating the Relationship**: We need to determine if the reason supports the assertion.
- **Explanation**: The reason that Bakelite is an infusible solid mass directly supports the assertion that Bakelite is a thermosetting polymer. The infusibility is a characteristic feature of thermosetting polymers, thus providing a correct explanation for the assertion.

5. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion.
- **Final Answer**: Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.