GKFix MCQ Question

Which of the following compounds is a complex and not a double salt?

• A. FeSO₄.(NH₄)₂SO₄.6H₂O
• B. KCl.MgCl₂.6H₂O
• C. KAl(SO₄)₂.12H₂O
• D. K₄[Fe(CN)₆]