Which among the following is NOT a use of sodium hydroxide?
(i) Used in making soaps and detergents.
(ii) Used in the manufacture of paper.
(iii) Used for removing permanent hardness of water.

Correct option is C

Correct option : (c)

(iii) Used for removing permanent hardness of water.

Information Booster:

 - (i) Used in making soaps and detergents: This is correct. Sodium hydroxide (NaOH) is a key ingredient in the process of making soap (saponification), where it reacts with fats and oils to produce soap and glycerol.

- (ii) Used in the manufacture of paper: This is correct. Sodium hydroxide is used in the pulping process for paper production. It helps break down lignin, which holds the fibers together in wood, making it easier to extract cellulose for papermaking.

- (iii) Used for removing permanent hardness of water: This is incorrect. Sodium hydroxide is not typically used for removing permanent hardness of water. Permanent hardness of water is usually removed by ion exchange methods or by adding washing soda (sodium carbonate), which precipitates the calcium and magnesium ions responsible for hardness. Sodium hydroxide is used for other purposes like cleaning and in industrial processes, but not for hardness removal.