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 $\displaystyle \mathrm{Na}_{2} \mathrm{SO}_{3}$ to (D). Identify (A), (B), (C) and (D).