Question

Which compound is insoluble in water? (1) KOH (3) Na3PO4 (2) NH4Cl (4) PbSO4

Answer 1

Ans: 4) PbSO4

Different compounds are soluble in water to a different extent, some of them are completely insoluble in water. Solubility rules help in identifying the water soluble and insoluble compounds.  

Based on the rules:

1) Salts of group IA (Li, Na, K, Rb and Cs) are soluble in water

2) Salts containing NH4+ ions are water soluble

3) All phosphates (PO4³⁻) are insoluble except those containing group IA elements and (NH4)₃PO4

4) All sulfates, SO4²⁻ salts are generally soluble with the exception of Ca2+, Sr2+, Ba2+, Hg₂²⁺, Hg2+, Pb2+ and Ag+

Therefore, among the given examples:

1) KOH contains group 1A (K) therefore soluble

2) Na3PO4 contains group IA element (Na), therefore soluble

3) NH4Cl contains NH4+ ion, therefore soluble

4) Sulfate of lead (Pb) is insoluble

Answer 2

The answer is (4) PbSO₄.