`CO_2` is given off by chemicals like :

Options

A. sodium bicarbonate
B. calcium sulphate
C. sodium sulphate
D. sulphuric acid

Explanation

To determine which chemicals give off carbon dioxide (CO₂), we will analyze each option provided:

### Step-by-Step Solution:

1. **Identify the Chemicals**: We have four chemicals to analyze:
- Sulfuric acid (H₂SO₄)
- Sodium sulfate (Na₂SO₄)
- Calcium sulfate (CaSO₄)
- Sodium bicarbonate (NaHCO₃)

2. **Analyze Sulfuric Acid (H₂SO₄)**:
- Sulfuric acid does not contain any carbon atoms in its formula.
- Therefore, it cannot produce carbon dioxide (CO₂).
- **Conclusion**: H₂SO₄ does not give off CO₂.

3. **Analyze Sodium Sulfate (Na₂SO₄)**:
- Sodium sulfate also does not contain any carbon atoms.
- Thus, it will not produce carbon dioxide (CO₂).
- **Conclusion**: Na₂SO₄ does not give off CO₂.

4. **Analyze Calcium Sulfate (CaSO₄)**:
- Calcium sulfate, like the previous two, does not have any carbon atoms.
- Hence, it cannot produce carbon dioxide (CO₂).
- **Conclusion**: CaSO₄ does not give off CO₂.

5. **Analyze Sodium Bicarbonate (NaHCO₃)**:
- Sodium bicarbonate contains carbon in its formula.
- When heated, it decomposes to form sodium carbonate (Na₂CO₃), carbon dioxide (CO₂), and hydrogen (H₂).
- The reaction can be summarized as:
\[ 2 \text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 + \text{H}_2 \]
- **Conclusion**: NaHCO₃ does give off CO₂.

6. **Final Answer**:
- The only chemical from the options that gives off carbon dioxide (CO₂) is **Sodium Bicarbonate (NaHCO₃)**.

### Summary:
- **Option 1 (Sodium Bicarbonate)** produces CO₂.
- **Options 2 (Sulfuric Acid), 3 (Sodium Sulfate), and 4 (Calcium Sulfate)** do not produce CO₂.