Which one of the following mixed sulphates is not an alum ?
K2SO4.Al2(SO4)3.24H2O
K2SO4.Cr2(SO4)3.24H2O
Na2SO4.Fe2(SO4)3.24H2O
CuSO4.Al2(SO4)3.24H2O
Alums contain monovalent (M+) and trivalent (M+3) ions. CuSO4.Al2(SO4)3.24H2O has Cu+2and Al+3ions