Assertion (A): A certain recation is catalysed by acids and the catalytic activity of `0.1M` solutions of the acids in water decrease in the order, `HCI, HCOOH`, and `CH_(3)COOH`. The same reaction takes place in anhydrous `NH_(3)`, but the three acids have same catalytic effect in `0.1M` solution.
Reason (R) : The order of catalytic activity in water is the same as the order of acidity. in anhyrous `NH_(3)`, all the three acids are strong.

Options

A. If both (A) and (R) are correc, and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.

Explanation

To solve the question, we need to analyze both the assertion (A) and the reason (R) provided and determine their validity and relationship.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the catalytic activity of `0.1M` solutions of the acids in water decreases in the order: `HCl > HCOOH > CH3COOH`.
- It also mentions that in anhydrous `NH3`, the three acids have the same catalytic effect in `0.1M` solution.

2. **Analyzing the Acids**:
- **HCl** (Hydrochloric acid) is a strong acid and dissociates completely in water.
- **HCOOH** (Formic acid) is a weak acid and does not dissociate completely.
- **CH3COOH** (Acetic acid) is also a weak acid and has a lower dissociation compared to formic acid.
- Thus, in water, the order of acidity is indeed `HCl > HCOOH > CH3COOH`, which supports the assertion.

3. **Understanding the Reason (R)**:
- The reason states that the order of catalytic activity in water is the same as the order of acidity, and in anhydrous `NH3`, all three acids are strong.
- In anhydrous `NH3`, the solvent (ammonia) has a lower acidity compared to the acids being tested, which means the acids behave similarly in terms of their catalytic activity.

4. **Comparison of Assertion and Reason**:
- The assertion is correct as it accurately describes the catalytic activity in water.
- The reason is also correct because it explains that in anhydrous `NH3`, the catalytic effect of the acids is similar due to their strong nature relative to the solvent.

5. **Conclusion**:
- Since both the assertion and the reason are correct, and the reason provides a correct explanation for the assertion, the correct answer is:
- **Option A**: Both assertion and reason are correct and reason is the correct explanation of assertion.