`HNO_(2)` acts as an oxidant with which one of the following reagent :-

Options

A. `KMnO_(4)`
B. `H_(2)S`
C. `K_(2)Cr_(2)O_(7)`
D. `Br_(2)`

Answer

To determine which reagent HNO₂ acts as an oxidant with, we need to analyze the oxidation states of the elements involved in each reaction. Let's go through the options step by step.

### Step 1: Analyze the oxidation state of HNO₂
HNO₂ (nitrous acid) has nitrogen in the +3 oxidation state. It can either be oxidized to HNO₃ (where nitrogen is +5) or reduced to NO (where nitrogen is +2) or even to N₂ (where nitrogen is 0).

### Step 2: Evaluate the reagents
1. **KMnO₄**:
- Manganese (Mn) in KMnO₄ has an oxidation state of +7. Since it is already at its highest oxidation state, it cannot be oxidized further. Therefore, HNO₂ cannot act as an oxidant here.

2. **H₂S**:
- In H₂S, sulfur (S) has an oxidation state of -2. When HNO₂ reacts with H₂S, sulfur can be oxidized to 0 (its oxidation state in elemental form), while HNO₂ can be reduced to NO (oxidation state +2). This indicates that HNO₂ is acting as an oxidant in this reaction.

3. **K₂Cr₂O₇** (Potassium dichromate):
- Chromium (Cr) in K₂Cr₂O₇ has an oxidation state of +6. Similar to KMnO₄, it is at a high oxidation state and can only be reduced to +3. Thus, HNO₂ cannot act as an oxidant here.

4. **Br₂** (Bromine):
- Bromine in Br₂ has an oxidation state of 0. When reacting with HNO₂, bromine can be reduced to Br⁻ (oxidation state -1) or to BrO₃⁻ (oxidation state +5). However, HNO₂ would be oxidized to HNO₃ (oxidation state +5), which means it cannot act as an oxidant.

### Step 3: Conclusion
From the analysis above, HNO₂ acts as an oxidant only when reacting with H₂S. In this reaction, H₂S is oxidized, and HNO₂ is reduced.

Thus, the correct answer is **H₂S** (Option B).

---