FeSO₄ solution and (NH₄)₂SO₄ solution are mixed in 1:1 molar ratio to form compound (A). Compound (A) does not give positive test for

FeSO₄(aq) + (NH₄)₂SO_4(aq) + 6H₂O $\to$FeSO₄.(NH₄)₂SO₄.6H₂O.

Mohr salt formed is double salt and ionizes completely in solution and forms ions,Fe⁺²,${\mathrm{NH}}_4^{+}$,${\mathrm{SO}}_4^{-2}$