Solution of a salt in dil `H_(2)SO_(4)` produces deep blue colour with starch iodide solution .The salt contains

Options

A. `Br^(Theta)`
B. `I^(Theta)`
C. `NO_(2)^(Theta)`
D. `NO_(3)^(Theta)`

Answer

To determine the composition of the salt that produces a deep blue color with starch iodide solution upon reaction with dilute H₂SO₄, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When a salt is dissolved in dilute sulfuric acid (H₂SO₄), it may produce various ions. The key observation is the formation of a deep blue color with starch iodide solution.

2. **Identifying Possible Ions**:
- The options given are bromide ion (Br⁻), iodide ion (I⁻), nitrite ion (NO₂⁻), and nitrate ion (NO₃⁻). We need to determine which of these ions can react with starch iodide to produce a blue color.

3. **Analyzing Nitrite Ion (NO₂⁻)**:
- When nitrite ions (from sodium nitrite, NaNO₂) are treated with dilute H₂SO₄, they form nitrous acid (HNO₂).
- The reaction can be represented as:
\[ \text{NaNO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{HNO}_2 \]

4. **Decomposition of Nitrous Acid**:
- Nitrous acid (HNO₂) can decompose to produce nitrogen oxides (NO and NO₂):
\[ 3 \text{HNO}_2 \rightarrow 2 \text{NO} + \text{HNO}_3 + \text{H}_2\text{O} \]

5. **Oxidation of Nitric Oxide (NO)**:
- The nitrogen monoxide (NO) can further react with oxygen to produce nitrogen dioxide (NO₂):
\[ 2 \text{NO} + \text{O}_2 \rightarrow 2 \text{NO}_2 \]

6. **Reaction with Iodide Ion**:
- The nitrogen dioxide (NO₂) can react with iodide ions (I⁻) to liberate iodine (I₂):
\[ 2 \text{KI} + 2 \text{NO}_2 \rightarrow 2 \text{KNO}_2 + \text{I}_2 \]

7. **Formation of Blue Color**:
- The liberated iodine (I₂) then reacts with starch to form a blue complex, which is the deep blue color observed.

8. **Conclusion**:
- Since the deep blue color is produced due to the presence of iodine, and the only ion that can lead to this reaction when treated with dilute H₂SO₄ is the nitrite ion (NO₂⁻), we conclude that the salt contains the nitrite ion.

### Final Answer:
The salt contains the **nitrite ion (NO₂⁻)**.