Salt +`H_(2)SO_(4)` (dilute) `to` Coloured vapours which turns starch iodide paper blue.Identify the acid radical and the coloured vapours giving the relevant chemical equations.

Answer

To solve the problem, we need to identify the acid radical and the colored vapors produced when a salt reacts with dilute sulfuric acid (H₂SO₄).

### Step-by-Step Solution:

1. **Identify the Salt**:
The salt mentioned in the question is likely a nitrite salt, such as sodium nitrite (NaNO₂) or potassium nitrite (KNO₂). The nitrite ion (NO₂⁻) is the key component here.

2. **Reaction with Dilute Sulfuric Acid**:
When the nitrite salt reacts with dilute sulfuric acid, the following reaction occurs:
\[ \text{NaNO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{HNO}_2 \]
Here, HNO₂ (nitrous acid) is formed.

3. **Decomposition of Nitrous Acid**:
The nitrous acid (HNO₂) can decompose to produce nitric oxide (NO) and other products:
\[ 3\text{HNO}_2 \rightarrow \text{HNO}_3 + 2\text{NO} + \text{H}_2\text{O} \]
This reaction indicates that HNO₂ can yield nitric oxide (NO).

4. **Formation of Colored Vapors**:
The nitric oxide (NO) can further react with oxygen (O₂) in the air to form nitrogen dioxide (NO₂), which is a brown gas:
\[ 2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2 \]
The colored vapors produced here are nitrogen dioxide (NO₂).

5. **Reaction with Starch Iodide Paper**:
The nitrogen dioxide (NO₂) can react with potassium iodide (KI) to produce iodine (I₂), which turns starch iodide paper blue:
\[ 2\text{KI} + 2\text{NO}_2 \rightarrow 2\text{KNO}_2 + \text{I}_2 \]
The iodine (I₂) reacts with starch to give a blue color.

### Summary:
- **Acid Radical**: NO₂⁻ (Nitrite ion)
- **Colored Vapors**: NO₂ (Nitrogen dioxide)

### Relevant Chemical Equations:
1. \(\text{NaNO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{HNO}_2\)
2. \(3\text{HNO}_2 \rightarrow \text{HNO}_3 + 2\text{NO} + \text{H}_2\text{O}\)
3. \(2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2\)
4. \(2\text{KI} + 2\text{NO}_2 \rightarrow 2\text{KNO}_2 + \text{I}_2\)