Acetic acid is a weak acid because

Options

A. its aqueous solution is acidic
B. it is highly ionised
C. it is weakly ionised
D. it contains - COOH group .

Explanation

### Step-by-Step Solution:

1. **Identify the Compound**: The compound in question is Acetic Acid, which has the chemical formula \( \text{CH}_3\text{COOH} \).

2. **Understand the Nature of Acetic Acid**: Acetic Acid is classified as a weak acid. This classification is based on its ability to ionize in water.

3. **Ionization in Water**: When Acetic Acid is dissolved in water, it partially dissociates into ions. The dissociation can be represented as:
\[ \text{CH}_3\text{COOH} \rightleftharpoons \text{CH}_3\text{COO}^- + \text{H}^+ \]
This means that only a small fraction of the Acetic Acid molecules ionize to form acetate ions (\( \text{CH}_3\text{COO}^- \)) and hydrogen ions (\( \text{H}^+ \)).

4. **Conclusion on Weak Acid Nature**: Since Acetic Acid only partially ionizes in solution, it is classified as a weak acid. This is the reason why Acetic Acid is considered a weak acid.

5. **Final Statement**: Therefore, Acetic Acid is a weak acid because it is weakly ionized in water.