Answer : 4. "Sulphuric acid"
Explanation :

Answer: D) Sulphuric acid Explanation: Sulphuric acid is called the King of Chemicals because it is used in the preparation of a very large number of other useful chemicals such as hydrochloric acid, nitric acid, dyes, drugs etc. In fact the annual production of shulpuric acid in a country is a measure of the economy of the country.