Question

A gas when passed through K₂Cr₂O₇ and dil. H₂SO₄ solution turns it green, the gas is

(A) CO₂

(B) NH₃

(C) SO₂

(D) Cl₂

Answer 1

(C) SO₂ 
Sulphur dioxide gas is oxidized to sulphuric acid when passed through acidified
potassium dichromate solution. The colour of the solution changes from orange to
green because potassium dichromate is reduced to chromic sulphate.