By-product obtained by soap industry is A. caustic soda B. glycerol C. naphthalene D. caustic potash

The correct answer is: B. glycerol

Glycerol is a by-product of the soap industry. It is a colorless, odorless, viscous liquid that is sweet-tasting. It is used in a variety of products, including cosmetics, pharmaceuticals, and food.

Caustic soda (sodium hydroxide) and caustic potash (potassium hydroxide) are both used in the soapmaking process, but they are not by-products. They are the main ingredients in soap.

Naphthalene is a white, crystalline solid that is used in mothballs and other products. It is not a by-product of the soap industry.