Assertion: Agar is used to solidify the medium
Reason: Higher concentration of agar makes the medium hard and diffusion of nutrients in plant tissues may be checked.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true and the Reason is not the Reason is not the correct explanation of the assertion
C. If assertion is true but the Reason are false
D. If both Assertion and Reason are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Agar is used to solidify the medium."
- Agar is a polysaccharide obtained from red algae (specifically, agar-agar seaweed). When it is heated and then cooled, it forms a gel-like substance that solidifies the medium.
- Therefore, the assertion is **true**.

2. **Understanding the Reason**:
- The reason provided is "Higher concentration of agar makes the medium hard and diffusion of nutrients in plant tissues may be checked."
- It is true that increasing the concentration of agar results in a firmer gel, which can affect the pore size of the medium. A higher concentration of agar leads to smaller pore sizes, which can indeed slow down or check the diffusion of nutrients.
- Thus, the reason is also **true**.

3. **Evaluating the Relationship**:
- Although both the assertion and the reason are true, the reason does not correctly explain the assertion. The assertion is about the use of agar to solidify the medium, while the reason discusses the effects of agar concentration on nutrient diffusion.
- Therefore, while both statements are true, the reason is not the correct explanation for the assertion.

4. **Conclusion**:
- The final answer is: The assertion is true, the reason is true, but the reason is not the correct explanation for the assertion.

### Final Answer:
- Assertion: True
- Reason: True
- Explanation: The reason is not the correct explanation for the assertion.

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