Four pairs of aqueous solutions are mixed.
Which pair of solutions forms a blue precipitate?
FeSO4(aq)\text{FeSO}_4\text{(aq)}FeSO4(aq) and NaOH(aq)\text{NaOH(aq)}NaOH(aq)
FeCl3(aq)\text{FeCl}_3\text{(aq)}FeCl3(aq) and NaOH(aq)\text{NaOH(aq)}NaOH(aq)
CuSO4(aq)\text{CuSO}_4\text{(aq)}CuSO4(aq) and NaOH(aq)\text{NaOH(aq)}NaOH(aq)
NH4Cl(aq)\text{NH}_4\text{Cl(aq)}NH4Cl(aq) and NaOH(aq)\text{NaOH(aq)}NaOH(aq)
