Question

Why does a lump of cotton wool shrink in water ?​

Answer 1

A lump of cotton wool has a lot of air trapped inside the space present in its fibers. When this lump of cotton is immersed in water, all the air is replaced by water. Due to this, the cotton lump shrinks down.

Answer 2

A lump of cotton has a lot of air inside it and when we dip it inside the water the air escapes from the cotton and the cotton absorbs the water when it absorbs the water the starts to become heavy and shrinks in the water