What is observed when acetic acid and sodium bicarbonate solution are mixed?

Options

A. A colourless odourless gas is liberated.
B. A colourless gas that turns blue litmus red.
C. A colourless gas which burns with a soap sound.
D. Both (a) and (b).

Explanation

### Step-by-Step Solution

1. **Identify the Reactants**: The two reactants involved in this reaction are acetic acid (CH₃COOH) and sodium bicarbonate (NaHCO₃).

2. **Write the Chemical Reaction**: When acetic acid reacts with sodium bicarbonate, the following chemical reaction occurs:
\[ \text{CH}_3\text{COOH} + \text{NaHCO}_3 \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2 \]
Here, sodium acetate (CH₃COONa), water (H₂O), and carbon dioxide (CO₂) are produced.

3. **Observe the Products**:
- **Sodium Acetate**: This is a salt formed from the reaction.
- **Water**: This is a liquid that is formed as a byproduct.
- **Carbon Dioxide**: This gas is evolved during the reaction.

4. **Identify Physical Observations**:
- The evolution of carbon dioxide gas can be observed as bubbles or fizzing in the solution.
- The solution may become slightly warmer due to the reaction.

5. **Test for Acidity**:
- The carbon dioxide gas produced can be tested for its acidic nature by passing it through wet litmus paper.
- The blue litmus paper will turn red, indicating the presence of an acid (carbonic acid formed when CO₂ dissolves in water).

### Summary of Observations
- **Bubbles/Fizzing**: Indicates the release of carbon dioxide gas.
- **Color Change of Litmus Paper**: Blue litmus turns red, confirming the acidic nature of the gas.