When chromite ore ${\mathrm{FeCr}}_2{\mathrm{O}}_4$ is fused with $\mathrm{NaOH}$ in presence of air, a yellow coloured compound
(A) is obtained which on acidification with dilute sulphuric acid gives a compound (B). Compound
(B) on reaction with $\mathrm{KCl}$ forms a orange coloured crystalline compound (C).
(i) Write the formulae of the compounds (A), (B) and (C).
(ii) Write one use of compound (C).
OR
Complete the following chemical equations:
(i) ${\mathrm{MnO}}_4^{-}+3{\mathrm{S}}_2{\mathrm{O}}_3^{2-}+{\mathrm{H}}_2\mathrm{O}\to$ ?
(ii) ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+3{\mathrm{Sn}}^{2+}+14{\mathrm{H}}^{+}\to$ ?