Assertion (A): `HNO_(3)` acts only as an oxidising agent, while `HNO_(2)` acts both as an oxidising agnet and a reducing agent.
Reason (R ): The oxidation number of `N` in `HNO_(3)` is mximum.

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)` 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 `HNO3` acts only as an oxidizing agent, while `HNO2` acts both as an oxidizing agent and a reducing agent.
- To validate this, we need to look at the oxidation states of nitrogen in both compounds.

2. **Calculating the Oxidation State of Nitrogen**:
- For `HNO3`:
- The oxidation state of nitrogen (N) can be calculated as follows:
- Let the oxidation state of N be x.
- The overall charge of the molecule is neutral (0).
- The equation is: 1 (for H) + x (for N) + 3*(-2) (for O) = 0
- This simplifies to: 1 + x - 6 = 0 → x = +5.
- Therefore, the oxidation state of N in `HNO3` is +5.

- For `HNO2`:
- Similarly, we calculate the oxidation state of nitrogen:
- Let the oxidation state of N be y.
- The equation is: 1 (for H) + y (for N) + 2*(-2) (for O) = 0
- This simplifies to: 1 + y - 4 = 0 → y = +3.
- Therefore, the oxidation state of N in `HNO2` is +3.

3. **Analyzing the Behavior of `HNO3`**:
- Since the oxidation state of nitrogen in `HNO3` is +5 (the highest oxidation state for nitrogen), it cannot be oxidized further. Thus, `HNO3` can only act as an oxidizing agent because it can accept electrons from other substances.

4. **Analyzing the Behavior of `HNO2`**:
- The oxidation state of nitrogen in `HNO2` is +3. This means it can either be oxidized to +5 (acting as a reducing agent) or reduced to a lower oxidation state (acting as an oxidizing agent). Therefore, `HNO2` can act both as an oxidizing agent and a reducing agent.

5. **Understanding the Reason (R)**:
- The reason states that the oxidation number of N in `HNO3` is maximum.
- This is correct, as we calculated the oxidation state of N in `HNO3` to be +5, which is indeed the maximum oxidation state for nitrogen.

6. **Conclusion**:
- Both the assertion and the reason are correct.
- The reason provided is a correct explanation for the assertion.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the reason is the correct explanation of the assertion.