Which of the following statements about the reaction is`//`are correct?
`HgS+HCl+HNO_(3)rarrH_(2)HgCl_(4)+NO+S+H_(2)O`

Options

A. `Hg` is reduced.
B. Sulphide is oxidised.
C. `N` is reduced
D. `HNO_(3)` is an oxidant.

Explanation

To analyze the given redox reaction and determine which statements are correct, we will follow these steps:

### Step 1: Write the reaction and identify the species involved.
The reaction is:
\[ \text{HgS} + \text{HCl} + \text{HNO}_3 \rightarrow \text{H}_2\text{HgCl}_4 + \text{NO} + \text{S} + \text{H}_2\text{O} \]

### Step 2: Assign oxidation states to the relevant elements.
- **Mercury (Hg)** in HgS:
- In HgS, Hg has an oxidation state of +2 (since S is -2).
- **Mercury (Hg)** in H₂HgCl₄:
- Let the oxidation state of Hg be \( x \).
- The equation is: \( 2 + x + 4(-1) = 0 \)
- Solving gives \( x = +2 \).

- **Sulfur (S)** in HgS:
- In HgS, S has an oxidation state of -2.
- **Sulfur (S)** in elemental S:
- In elemental S, the oxidation state is 0.

- **Nitrogen (N)** in HNO₃:
- In HNO₃, N has an oxidation state of +5.
- **Nitrogen (N)** in NO:
- In NO, N has an oxidation state of +2.

### Step 3: Determine changes in oxidation states.
- **Mercury (Hg)**: +2 to +2 (no change, not reduced).
- **Sulfur (S)**: -2 to 0 (oxidized).
- **Nitrogen (N)**: +5 to +2 (reduced).

### Step 4: Identify the oxidizing and reducing agents.
- **Oxidizing agent**: HNO₃ (as it gets reduced from +5 to +2).
- **Reducing agent**: HgS (as it gets oxidized).

### Step 5: Evaluate the statements.
1. **Hg is reduced**: False (Hg remains +2).
2. **Sulfide is oxidized**: True (S changes from -2 to 0).
3. **Nitrogen is reduced**: True (N changes from +5 to +2).
4. **HNO₃ is an oxidant**: True (it is reduced, thus acts as an oxidant).

### Conclusion:
The correct statements are:
- Sulfide is oxidized (True).
- Nitrogen is reduced (True).
- HNO₃ is an oxidant (True).

Thus, the correct options are B, C, and D.

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