Pick out the statement which is not relevant in the discussion of colloids

Options

A. Sodium aluminium silicate is used in the softening of hard water
B. Potash alum is used in shaving and as a antiseptic in medicine
C. Artificial rain is caused by throwing electrified sand on the clouds from an aeroplane
D. Deltas are formed at a place where the river pours its water into the sea

Explanation

Softening of hard water by use of sodium aluminium silicate involve ion exchange.