Name the acid formed when sulphur dioxide dissolves in water.

When sulfur dioxide (\( \text{SO}_2 \)) dissolves in water, it forms sulfurous acid (\( \text{H}_2\text{SO}_3 \)). The chemical reaction can be represented as follows:

\[
\text{SO}_2 (g) + \text{H}_2\text{O} (l) \rightarrow \text{H}_2\text{SO}_3 (aq)
\]

### Explanation:

1. **Dissolution Process**: When sulfur dioxide gas comes into contact with water, it dissolves in the water.

2. **Formation of Sulfurous Acid**: During the dissolution, sulfur dioxide reacts with water to produce sulfurous acid. This acid is a weak acid and can further dissociate into bisulfite ions (\( \text{HSO}_3^- \)) and sulfite ions (\( \text{SO}_3^{2-} \)) when in solution.

3. **Acidic Properties**: Sulfurous acid is responsible for the acidic properties of solutions containing dissolved sulfur dioxide, which can affect the pH of the solution.

In summary, the acid formed when sulfur dioxide dissolves in water is sulfurous acid (\( \text{H}_2\text{SO}_3 \)).