Which of the following statements regarding air is incorrect?

Options

A. Air contains dust particles and water vapour.
B. Air neither has fixed shape nor has fixed volume.
C. Air has mass and occupies space.
D. Air is incompressible.

Explanation

To determine which statement regarding air is incorrect, we will analyze each statement provided:

1. **Air contains dust particles and water vapours.**
- This statement is **correct**. Air is a mixture of gases and can carry dust particles and water vapours.

2. **Air neither has fixed shape nor fixed volume.**
- This statement is also **correct**. Air, like other gases, does not have a definite shape or volume; it takes the shape and volume of its container.

3. **Air has mass and occupies space.**
- This statement is **correct**. Air is made up of particles that have mass, and it occupies space.

4. **Air is incompressible.**
- This statement is **incorrect**. Air is a gas, and gases are highly compressible. This means that the volume of air can change significantly when pressure is applied.

Based on this analysis, the incorrect statement regarding air is: **"Air is incompressible."**

### Step-by-Step Solution:
1. **Identify the statements about air.**
- List the statements provided in the question.

2. **Evaluate each statement for correctness.**
- Check if air contains dust and water vapours (correct).
- Check if air has a fixed shape and volume (incorrect).
- Check if air has mass and occupies space (correct).
- Check if air is incompressible (incorrect).

3. **Determine which statement is incorrect.**
- Conclude that the statement "Air is incompressible" is incorrect.

4. **State the final answer.**
- The incorrect statement is: **"Air is incompressible."**