Assertion (A) Thermosetting polymers undergo permanent change on heating.
Reason(R ) On heating, extensive cross-links formed between polymer chains.

Options

A. Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion
C. Assertion is correct but Reason is incorrect
D. Assertion is incorrect and Reason is correct

Answer

To analyze the assertion and reason provided in the question, we can break it down step by step:

### Step 1: Understanding the Assertion
- **Assertion (A)** states that "Thermosetting polymers undergo permanent change on heating."
- **Explanation**: Thermosetting polymers, such as Bakelite, are materials that, once set into a shape through heat and pressure, cannot be remolded or reshaped upon further heating. This is due to the irreversible chemical changes that occur during the curing process.

### Step 2: Understanding the Reason
- **Reason (R)** states that "On heating, extensive cross-links formed between polymer chains."
- **Explanation**: When thermosetting polymers are heated, they undergo a curing process where the polymer chains form extensive cross-links. These cross-links create a three-dimensional network structure that stabilizes the polymer. This network prevents the polymer from melting or reshaping upon subsequent heating.

### Step 3: Analyzing the Relationship
- Both the assertion and the reason are correct statements about thermosetting polymers.
- The reason provided (formation of cross-links) directly explains why the assertion (permanent change on heating) is true. The formation of cross-links is what makes the change permanent and irreversible.

### Conclusion
- Both the assertion and the reason are correct, and the reason is indeed the correct explanation of the assertion.

### Final Answer
- **Both Assertion (A) and Reason (R) are correct, and R is the correct explanation of A.**

---