Assertion: Benzoic acid is a weaker acid than formic acid
Reason: Phenyl group when attached to carbonyl group becomes electron donating.

Options

A. if both assertion and reson are true, and reason is the true explanation of the assertion.
B. If both assertion and reason are true, but reason is not the true explanation of the assertion.
C. if assertion is true, but reason is false.
D. If both assertion and reason are false.

Answer

To determine whether the assertion and reason provided in the question are true, we will analyze both statements step by step.

### Step 1: Understand the Assertion
The assertion states that "Benzoic acid is a weaker acid than formic acid."

- **Benzoic Acid Structure**: The structure of benzoic acid is represented as C6H5COOH, where the carboxylic acid (-COOH) group is attached to a phenyl ring (C6H5).
- **Formic Acid Structure**: The structure of formic acid is HCOOH, which has a carboxylic acid group directly attached to a hydrogen atom.

### Step 2: Compare Acidity
To compare the acidity of benzoic acid and formic acid, we need to consider the stability of their conjugate bases after they donate a proton (H+).

- **Conjugate Base of Benzoic Acid**: When benzoic acid donates a proton, it forms the benzoate ion (C6H5COO^-). The negative charge on the oxygen can be delocalized into the phenyl ring, but the phenyl ring is an electron-donating group. This means it can destabilize the negative charge on the oxygen due to increased electron density.

- **Conjugate Base of Formic Acid**: When formic acid donates a proton, it forms the formate ion (HCOO^-). In this case, there are no electron-donating groups attached to the carboxylate ion, allowing for better stabilization of the negative charge through resonance.

### Step 3: Conclusion on Acidity
The stability of the conjugate base is crucial for acidity. Since the benzoate ion is less stable due to the electron-donating effect of the phenyl group, benzoic acid is indeed a weaker acid than formic acid. Therefore, the assertion is true.

### Step 4: Understand the Reason
The reason states that "The phenyl group when attached to the carbonyl group becomes electron donating."

- The phenyl group (C6H5) is known to be an electron-donating group through resonance. When attached to the carbonyl group (C=O), it can push electron density towards the carbonyl carbon, which can destabilize the negative charge on the conjugate base formed after deprotonation.

### Step 5: Conclusion on Reason
Since the reason correctly explains why benzoic acid is a weaker acid than formic acid, it is also true.

### Final Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion.