. The chemical substance used for removal of permanent hardness of water is
(a) bleaching powder.
(b) washing soda.
(c) baking soda.
(d) plaster of Paris.
Explanation: In this process, hard water is treated with a calculated amount of washing soda (Na2CO3), so that chlorides and sulphates of calcium and magnesium present in hard water get precipitated as insoluble calcium and magnesium carbonates that can be easily filtered off.