Which one of the following compounds is insoluble in water?

A. Na2CO3

B. CaCO3

C. K2SO4

D. Fe(NO3)3

E. AgNO3

Answer:- B. CaCO3

The correct answer is ‘CaCO3.’ Solubility rules state that all carbonates are insoluble, with the exception of those containing Group I elements (Li, Na, K, Rb, Cs) and ammonium (NH4+). Calcium carbonate is therefore insoluble in water.

The other compounds are all soluble in water. (NH4)2S is soluble because all ammonium salts are soluble. NaOH is soluble because all alkali metal hydroxides are soluble. Ag2SO4 is soluble because all sulfates are soluble, with the exception of those containing Ca, Sr, Ba, Pb, and Ag. Pb(CH3COO)2 is soluble because all acetates are soluble.