On addition of conc. `H_2SO_4` to a chloride salt, colourless fumes are evolved but in case of iodide salt, violet fumes come out. This is because

Options

A. `H_2SO_4` reduces HI to `I_2`
B. HI is of violet colour
C. HI gets oxidised to `I_2`
D. HI changes to `HIO_3`

Explanation

To answer the question regarding the evolution of colorless fumes from chloride salts and violet fumes from iodide salts upon the addition of concentrated sulfuric acid (H₂SO₄), we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding the Reaction with Chloride Salts:**
- When a chloride salt, such as sodium chloride (NaCl), is treated with concentrated sulfuric acid (H₂SO₄), the following reaction occurs:
\[ \text{NaCl} + \text{H}_2\text{SO}_4 \rightarrow \text{HCl} + \text{Na}_2\text{SO}_4 \]
- In this reaction, hydrogen chloride (HCl) gas is produced, which is colorless. Therefore, the evolution of colorless fumes is due to the formation of HCl gas.

2. **Understanding the Reaction with Iodide Salts:**
- When an iodide salt, such as sodium iodide (NaI), is treated with concentrated sulfuric acid, the reaction is more complex:
\[ \text{NaI} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{HI} \]
- Initially, hydrogen iodide (HI) is formed. However, HI can further react with sulfuric acid:
\[ \text{HI} + \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{O} + \text{SO}_2 + \text{I}_2 \]
- In this reaction, iodine (I₂) is produced, which is violet in color. Therefore, the evolution of violet fumes is due to the formation of iodine gas.

3. **Oxidation-Reduction Process:**
- In the reaction involving iodide, HI acts as a reducing agent. It reduces sulfuric acid (H₂SO₄) from a higher oxidation state of sulfur (+6 in H₂SO₄) to a lower oxidation state (+4 in SO₂) while being oxidized to iodine (I₂).
- The oxidation states change as follows:
- Iodine in HI is in the -1 oxidation state and gets oxidized to 0 in I₂.
- Sulfur in H₂SO₄ is reduced from +6 to +4 in SO₂.

4. **Conclusion:**
- The colorless fumes from chloride salts are due to HCl gas, while the violet fumes from iodide salts are due to the formation of iodine gas (I₂) as a result of the oxidation of HI.

### Final Answer:
The colorless fumes from chloride salts are due to the formation of HCl gas, while the violet fumes from iodide salts are due to the formation of iodine gas (I₂) as HI is oxidized.

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