When FeCr_2 O_4 is fused with Na_2 CO_3 in the presence of air it gives a yellow solution of compound (A). Compound (A) on acidification gives…

When $\displaystyle \mathrm{FeCr}_{2} \mathrm{O}_{4}$ is fused with $\displaystyle \mathrm{Na}_{2} \mathrm{CO}_{3}$ in the presence of air it gives a yellow solution of compound (A). Compound (A) on acidification gives compound (B). Compound (B) on reaction with KCl forms an orange coloured (C). An acidified solution of compound (C) oxidises iodide to (D). Identify (A), (B), (C) and (D).