When chromite ore is fused 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 forms a orange coloured crystalline compound (C).

A. Write the formulae of the compounds (A), (B) and (C)

B. Write one use of compound (C).

When FeCr₂O₄ is fused with NaOH in presence of air, the resultant is Sodium Chromate (Na₂CrO₄):

4FeCr₂O₄ + 16NaOH +7O₂→8Na₂CrO₄ + 2Fe₂O₃ + 8H₂O

Hence A = Na₂CrO₄

Sodium Chromate upon acidification with dilute sulphuric acid gives sodium dichromate:

2Na₂CrO₄ + H₂SO₄→Na₂Cr₂O₇ + Na₂SO₄ +H₂O

Hence B = Na₂Cr₂O₇

Sodium Dichromate reacts with potassium chloride (KCl) to give potassium dichromate which an orange coloured crystalline compound:

Na₂Cr₂O₇ + 2KCl→ K₂Cr₂O₇ + 2NaCl

Hence C = Na₂Cr₂O₇

Potassium Dichromate is used as a precursor to potassium chrome alum and also used in leather tanning. It is also used as an oxidizing agent.