Question

When a crystal of copper sulphate is placed at the bottom of a beaker containing water, the water slowly turns blue. Why ?

Answer 1

Crystals of copper sulphate are blue.When these crystals are kept at the bottom of beaker containing water, the water slowly turns blue.This is because of diffusion of particles of copper sulphate with the particles of water.The mixing of copper sulphate and water continue till the whole solution turns blue.
OR
The spreading of blue colour of copper sulphate into water, on its own, is due to the diffusion of copper sulphate particles into water.