ANS:A - dialysis

Colloids can be purified by dialysis. Dialysis involves the separation of colloidal particles from the dispersing medium by allowing them to pass through a semi-permeable membrane. This membrane allows only the solvent molecules (usually water) and smaller solute particles to pass through while retaining the colloidal particles and larger solute particles. As a result, the colloidal particles are effectively separated from the dispersing medium, leading to purification.