Assertion `(A)`: Colour of `KMnO_4` disappears when dihydrogen gas is bubbled through it.
Reason `(R)` :Dihydrogen gas is highly inflammable.

Options

A. If both (A) and (R) are correct 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 assertion and reason question, we will analyze both the assertion (A) and the reason (R) separately.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the color of KMnO4 disappears when dihydrogen gas is bubbled through it.
- KMnO4 (Potassium permanganate) is a strong oxidizing agent and has a characteristic deep purple color in solution.

2. **Analyzing the Reaction**:
- When dihydrogen gas (H2) is bubbled through an aqueous solution of KMnO4, there is no significant reaction that occurs under normal conditions.
- Hydrogen gas does not react with KMnO4 in a way that would lead to the decolorization of the solution. Therefore, the assertion that the color disappears is incorrect.

3. **Understanding the Reason (R)**:
- The reason states that dihydrogen gas is highly inflammable.
- This is a true statement. Dihydrogen gas is indeed highly combustible and can react with oxygen to form water, releasing a large amount of energy in the process.

4. **Conclusion**:
- Since the assertion (A) is false (the color of KMnO4 does not disappear when H2 is bubbled through it), and the reason (R) is true (H2 is highly inflammable), we conclude that the correct answer is that the assertion is incorrect while the reason is correct.

### Final Answer:
- The assertion (A) is false, and the reason (R) is true.