Why does a lump of cotton wool shrink in water?

Explanation

### Step-by-Step Solution:

1. **Understanding Cotton Wool**:
- Cotton wool is a soft and fluffy material made up of fibers. These fibers have spaces between them that trap air, making the cotton wool appear fluffy.

2. **Cotton Wool in Water**:
- When a lump of cotton wool is placed in water, it is submerged in a liquid that is denser than the air trapped within it.

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