Which of the following pair of salts produce odourless gas with dil `H_(2)SO_(4)`?

Options

A. `HCO_(3)^(-) and HSO_(3)^(-)`
B. `HCO_(3)^(-) and CO_(3)^(2-)`
C. `S_(2)O_(3)^(2-) and CH_(3)CO_(2)^(-)`
D. `CO_(3)^(2-) and CH_(3)CO_(2)^(-)`

Answer

To solve the question of which pair of salts produces an odorless gas when reacted with dilute H₂SO₄, we will analyze each pair of salts provided in the options.

### Step-by-Step Solution:

1. **Identify the Salts in Each Pair:**
- Pair 1: Sodium bicarbonate (NaHCO₃) and Sodium bisulfite (NaHSO₃)
- Pair 2: Sodium bicarbonate (NaHCO₃) and Sodium carbonate (Na₂CO₃)
- Pair 3: Sodium thiosulfate (Na₂S₂O₃) and Sodium acetate (CH₃COONa)
- Pair 4: Calcium carbonate (CaCO₃) and Sodium acetate (CH₃COONa)

2. **Reaction of Sodium Bicarbonate with Dilute H₂SO₄:**
- NaHCO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂↑
- The gas produced is CO₂, which is odorless.

3. **Reaction of Sodium Bisulfite with Dilute H₂SO₄:**
- NaHSO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂↑
- The gas produced is SO₂, which has a pungent smell.

4. **Reaction of Sodium Carbonate with Dilute H₂SO₄:**
- Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂↑
- The gas produced is CO₂, which is odorless.

5. **Reaction of Sodium Thiosulfate with Dilute H₂SO₄:**
- Na₂S₂O₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂↑ + S (solid)
- The gas produced is SO₂, which has a pungent smell.

6. **Reaction of Sodium Acetate with Dilute H₂SO₄:**
- CH₃COONa + H₂SO₄ → Na₂SO₄ + H₂O + CH₃COOH
- The product acetic acid (CH₃COOH) has a vinegar-like smell.

7. **Reaction of Calcium Carbonate with Dilute H₂SO₄:**
- CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂↑
- The gas produced is CO₂, which is odorless.

### Conclusion:
From the analysis, the pairs that produce odorless gas (CO₂) when reacted with dilute H₂SO₄ are:
- Pair 1: Sodium bicarbonate and Sodium bisulfite (produces CO₂, but SO₂ is also produced)
- Pair 2: Sodium bicarbonate and Sodium carbonate (produces CO₂)
- Pair 4: Calcium carbonate and Sodium acetate (produces CO₂)

The correct answer is **Pair 2: Sodium bicarbonate and Sodium carbonate**.