Copper sulphate dissolves in `NH_(4)OH` solution but `FeSO_(4)` does not.

Answer

Copper sulphate dissolve in the ammonium hyroxide due to formation of a complex. Ferrous sulphate reacts with `NH_(4)OH` to form insoluble `Fe(OH)_(2)` . It does not any complex with `NH_(4)OH`.
`CuSO_(4)+4NH_(4)OH to [Cu(NH_(3))_(4)]So_(4)+4H_(2)O`
Deep blue solution
`FeSO_(4)+2NH_(4)OH to Fe(OH)_(2)+(NH_(4))_(2)SO_(4)`
Insoluble