When chromite ore `FeCr_(2)O_(4)` is fuse with 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 KCl formas an orange colured crystalline compound (C).
(i) Write the formulae of the compounds (A),(B) and (C).
(ii) Write one use of compounds (C).

Explanation

(i) `4FeCr_(2)O_(4) + 16 NaOH + 7O_(2) rarr underset("(A)(Sodium chromate")(8 Na_(2)CrO_(4))+ 2Fe_(2)O_(3)+ 8 H_(2)O`
`2Na_(2)CrO_(4) + H_(2)SO_(4) rarr underset("(B) Sodium dichromate")(Na_(2) Cr_(2)O_(7)) + Na_(2)SO_(4)+ H_(2)O`
`Na_(2)Cr_(2)O_(7) + 2KCl rarr underset("(C ) Potassium dichromate")( K_(2)Cr_(2) O_(7)) + 2NaCl`
(ii) Potassium dichromate is used as a powerful oxidizing agent in industries and in the tanning of leather.