Assertion: p-Chlorobenzoic acid is stronger than benzoic acid.
Reason: Chlorine has electron-donating resonance `(+R)`- effect.

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.

Explanation

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

### Step 1: Understand the Assertion
The assertion states that p-Chlorobenzoic acid is stronger than benzoic acid.
- **Benzoic acid (C6H5COOH)** is a carboxylic acid with a phenyl group attached to the carboxyl group.
- **p-Chlorobenzoic acid (C6H4ClCOOH)** has a chlorine atom at the para position relative to the carboxyl group.

### Step 2: Analyze the Acidity
The strength of an acid is determined by its ability to donate a proton (H+). The stability of the conjugate base formed after the proton is lost is crucial in determining acidity.
- When benzoic acid donates a proton, it forms the benzoate ion (C6H5COO-).
- When p-chlorobenzoic acid donates a proton, it forms the p-chlorobenzoate ion (C6H4ClCOO-).

### Step 3: Consider the Effect of Chlorine
Chlorine is an electronegative atom and exhibits a -I (inductive) effect, which pulls electron density away from the carboxyl group. However, it also has a +R (resonance) effect due to its ability to donate electron density through resonance.
- The -I effect of chlorine stabilizes the conjugate base of p-chlorobenzoic acid more than the +R effect destabilizes it.

### Step 4: Conclusion on Acidity
Since the -I effect of chlorine is stronger than its +R effect, the conjugate base of p-chlorobenzoic acid is more stable than that of benzoic acid. Therefore, p-chlorobenzoic acid is indeed a stronger acid than benzoic acid.

### Step 5: Evaluate the Reason
The reason states that chlorine has an electron-donating resonance (+R) effect. This statement is misleading because while chlorine does have a +R effect, its -I effect is more significant in this context, making the reasoning incorrect.

### Final Conclusion
- **Assertion**: True (p-Chlorobenzoic acid is stronger than benzoic acid).
- **Reason**: False (Chlorine's -I effect dominates over its +R effect).

### Answer
The correct answer is that the assertion is true, but the reason is false.

---