Assertion: (A): The reactions between `NH_(3)` and `MnO_(4)^(ө)` occurs in an acidic medium.
`NH_(3)+MnO_(4)^(ө)rarrMnO_(2)+NO_(2)`
Reason (R ): `MnO_(4)^(ө)` is reduced to `MnO_(2)` in acidic medium.

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 both `(A)` and `(R )` are incorrect.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that the reaction between `NH3` and `MnO4^(-)` occurs in an acidic medium.
- The reaction given is:
\[ NH_3 + MnO_4^{-} \rightarrow MnO_2 + NO_2 \]
- We need to determine if this reaction indeed occurs in an acidic medium.

2. **Analyzing the Reaction**:
- The reaction involves the oxidation of ammonia (`NH3`) and the reduction of permanganate ion (`MnO4^(-)`).
- In acidic medium, `MnO4^(-)` is typically reduced to `Mn^2+`, not `MnO2`.

3. **Understanding the Reason (R)**:
- The reason states that `MnO4^(-)` is reduced to `MnO2` in acidic medium.
- This is incorrect because `MnO4^(-)` does not get reduced to `MnO2` in acidic conditions; it reduces to `Mn^2+`.

4. **Conclusion**:
- Since the assertion is incorrect (the reaction does not occur in acidic medium) and the reason is also incorrect (the product of the reduction of `MnO4^(-)` in acidic medium is not `MnO2`), we conclude that both the assertion and the reason are false.

### Final Answer:
Both the assertion (A) and the reason (R) are incorrect.