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

• Correct answer
  A

  sodium aluminium silicate is used in the softening of hard water.
• B

  potash alum is used in shaving rounds and as a styptic 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.

Hence, the correct answer is option: 'A'.