Assertion : Phenol is a weak acid than ethanol.
Reason : Groups with + M effect and -I effect decrease acidity at p-position.

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 but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false
D. If the assertion and reason both are false

Answer

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Phenol is a weaker acid than ethanol."
- To evaluate this, we need to consider the acidity of both compounds. Phenol (C6H5OH) can donate a proton (H+) to form phenoxide ion (C6H5O-), while ethanol (C2H5OH) can donate a proton to form ethoxide ion (C2H5O-).
- The acidity of a compound is determined by the stability of its conjugate base.

2. **Analyzing the Conjugate Bases**:
- The conjugate base of phenol (phenoxide ion) is stabilized by resonance. The negative charge on the oxygen can be delocalized over the aromatic ring, which increases the stability of the phenoxide ion.
- The conjugate base of ethanol (ethoxide ion) does not have such resonance stabilization. The negative charge is localized on the oxygen atom, making it less stable compared to phenoxide ion.

3. **Comparing Acidity**:
- Since the phenoxide ion is more stable than the ethoxide ion, phenol is a stronger acid than ethanol. Thus, the assertion that "Phenol is a weaker acid than ethanol" is **false**.

4. **Understanding the Reason**:
- The reason states that "Groups with +M effect and -I effect decrease acidity at the para-position."
- The +M (mesomeric) effect refers to the electron-donating ability of groups through resonance, while the -I (inductive) effect refers to the electron-withdrawing ability of groups through sigma bonds.
- If a substituent with a +M effect is present at the para-position of a carboxylic acid, it can destabilize the conjugate base by increasing electron density, which can lead to decreased acidity.

5. **Evaluating the Reason**:
- The reasoning is correct. Substituents with +M and -I effects can indeed decrease the acidity of a compound by destabilizing the conjugate base, especially at the para-position.

6. **Conclusion**:
- The assertion is **false** and the reason is **true**. Therefore, the correct answer is that the assertion is false and the reason is true.

### Final Answer:
- **Assertion**: False
- **Reason**: True