Question

Which of the following forms a dirty green precipitate on reaction with caustic soda?

Options

• CuSO₄

• MgSO₄

• FeSO₄

• PbSO₄

Answer 1

FeSO₄

Explanation:

Ferrous sulphate (FeSO₄) reacts with caustic soda (NaOH) to form ferrous hydroxide [Fe(OH)₂], which is a dirty green precipitate.

\[\ce{FeSO4 ​+ 2NaOH → Fe(OH)2​↓ + Na2​SO4​}\]