A student carry out Qualitative Analysis test on hydrated salt and concluded that it contain K+, Cr3+, and SO42- ions?

The molar mass of anhydrous KCr(SO₄)₂ = (39.1 + 52.0 + 32.1×2 + 16.0×8) g/mol = 283.3 g/mol
The molar mass of KCr(SO₄)₂•nH₂O = 283.3 + n(1.0×2 + 16.0) g/mol = (283.3 + 18n) g/mol

The molar mass of KCr(SO₄)₂•nH₂O in g/mol:
283.3 + 18n = 499.3
18n = 216
n = 12

Hence, formula of the hydrated salt = KCr(SO₄)₂•12H₂O