Assertion : Solubility of alcohols in water decreases with the increase in the molecular mass.
Reason : The increase in the size of the alkyl group increases the polar nature of `O-H` group.

Options

A. If both assertion and reason are correct and reason is correct explanation for assertion.
B. If both assertion and reason are correct but reason is not correct explanation for assertion.
C. If assertion is correct but reason is incorrect.
D. If assertion and reason both are incorrect.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Analyze the Assertion
The assertion states: "Solubility of alcohols in water decreases with the increase in molecular mass."

- **Explanation**: This statement is true. As the molecular mass of alcohols increases, the hydrophobic (non-polar) character of the alkyl chain also increases. This leads to a decrease in solubility in water, which is a polar solvent. Therefore, the assertion is correct.

### Step 2: Analyze the Reason
The reason states: "The increase in the size of the alkyl group increases the polar nature of the `O-H` group."

- **Explanation**: This statement is incorrect. While the size of the alkyl group does increase, it does not enhance the polar nature of the `O-H` group. In fact, as the size of the alkyl group increases, the overall polarity of the molecule decreases because the larger alkyl group contributes more to the hydrophobic character of the alcohol. Thus, the reason is incorrect.

### Conclusion
- The assertion is correct, but the reason is incorrect. Therefore, the correct option is that the assertion is correct but the reason is incorrect.

### Final Answer
C: Assertion is correct, but reason is incorrect.

---