When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C ) can be crystallised from the solution. When compound (C ) is treated with KCl, orange crystals of compound (D) crystallise out. Identify A to D and also explain the reactions.

Explanation

The given data suggests that the process involves the preparation of potassium dichromate from chromite ore. The chemical reaction involved are as follows:
` underset("Chromite [A]")(4FeCr_(2)O_(4))+8Na_(2)CO_(3)+underset((Air))(7O_(2)) overset("(Fuse)") to underset("Sod.chromate(B)")(8Na_(2)CrO_(4))+2Fe_(2)O_(3)+8CO_(2)`
` underset((B))(2Na_(2)CrO_(4))+H_(2)SO_(4) to underset("Sod. dichromate(C)")(Na_(2)Cr_(2)O_(7)) +Na_(2)SO_(4)+H_(2)O`
` underset((C))(Na_(2)Cr_(2)O_(7))+2KCl to underset("(Orange crystal)") underset("Pot. dichromate (D)")(K_(2)Cr_(2)O_(7))+2NaCl`