Question

An aqueous solution of salt ‘R’ when treated with dil HCl, a
colourless gas is given out. The gas so evolved when passed
through acidified KMnO₄ decolourises KMnO₄ solution.
The salt ‘R’ is
(a) Na₂CO₃ (b) NaClO₃
(c) NaNO₂ (d) Na₂SO₃

Answer 1

Explanation:

Option @ is correct Na2Co3 .

Answer 2

The salt ‘R’ is

(d) Na₂SO₃

We know that the SO₂ gas decolourises acidified KMnO₄ solution, according to the reaction shown below.

2KMnO₄ + 2H₂O + 5SO₂ →2 H₂SO₄ + K₂SO₄ +2 MnSO₄

So the compound must have a sulphite group (SO₃²⁻) in order to liberate SO₂ gas.

Amongst the options given, Na₂SO₃ is the required answer.

Na₂SO₃ + 2HCl → 2NaCl  + H₂O + SO₂

Option (d) is correct.