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

`A= FeCr_(2)O_(4) ,B= Na_(2) CrO_(4) = Na_(2) Cr_(2)O_(7) .2H_(2)O, D=K_(2)Cr_(2)O_(7)`
Reactions`: underset((A))(4FeCr_(2)O_(4))+8Na_(2)CO_(3)+ 7O_(2)rarr underset((B))(Na_(2) CrO_(4))+2Fe_(2)O_(3)+8 CO_(2)`
`2Na_(2)CrO_(4)+H_(2)SO_(4) rarr underset((C ))(Na_(2)Cr_(2)O_(7)) + Na_(2)SO_(4)+H_(2)O`
`underset((C ))(Na_(2)Cr_(2)O_(7)) +2KCl rarr underset((D))(K_(2)Cr_(2)O_(7))+2NaCl`