Assertion : Sclerenchyma fibres constitute the major mechanical tissue of the plants.
Reason : The cells are thick walled and are made up of lignin.

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

To solve the question, we need to analyze the assertion and the reason given:

### Step 1: Understand the Assertion
The assertion states that "Sclerenchyma fibres constitute the major mechanical tissue of the plants."
- **Explanation**: Sclerenchyma fibers are indeed known for their role in providing mechanical support to plants. They are one of the key tissues that help maintain the structure and strength of various plant parts.

### Step 2: Understand the Reason
The reason given is "The cells are thick walled and are made up of lignin."
- **Explanation**: Sclerenchyma cells have thick walls that are often reinforced with lignin, which contributes to their strength and rigidity. This characteristic is essential for their function as mechanical support tissues.

### Step 3: Evaluate the Relationship
Now we need to determine if the reason provided is the correct explanation for the assertion.
- While both the assertion and reason are true, the reason does not fully explain why sclerenchyma fibers are considered the major mechanical tissue. The assertion focuses on their role in mechanical support, while the reason describes a structural feature (thick walls and lignin) that contributes to that role but does not explain it comprehensively.

### Conclusion
Based on the analysis:
- Both the assertion and reason are true.
- However, the reason is not the correct explanation of the assertion.

### Final Answer
The correct option is **B**: If both assertion and reason are true but reason is not the correct explanation of assertion.

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