Question

The sodium compound which is used for softening hard water:
(A) Washing soda
(B) Bleaching powder
(C) Caustic soda
(D) lime soda

Answer 1

Hint: Classification of water into two categories depending on its behavior towards soap solution is soft water and hard water. Water which produces lather with soap solution already is soft water. For example, distilled water and rainwater are common examples of soft water. Water which does not produce lather with soap solution easily is called hard water. For example, river water and seawater are common examples of hard water. The methods of hard water into soft water are softening methods.

Complete step by step answer:
Water to be used for various industrial purposes such as stream generation, brewing, dyeing, etc., should have no hardness or some specific hardness and should be free from certain impurities. For industrial purposes softening of water, the methods are removal of calcium and magnesium, certain cations in hard water.
(1) Desalination
(2) lime-soda process
(3) Zeolite process
(4) Ion-exchange process
(5) Washing soda method

Out of the various methods, the addition of washing soda to water can be a removal of hardness causing salts calcium and magnesium sulfates, chlorides. This process is called the washing soda method.
So, the given substances washing soda or sodium carbonate are the sodium compound used for the softening of hard water.
Bleaching powder formula - $CaOC{{l}_{2}}$
Lime soda - $Ca{{(OH)}_{2}}$
Caustic soda, NaOH is not used in the softening of hard water.

Note: The hardness of water effects on textile dyeing, washing, and finishing reaction. Hard water effects significantly in industries. Water usage in industries is very sensitive and hard water creates a plumbing problem which reduces flow through the pipes.