When $$MnO_2$$ and $$H_2SO_4$$ is added to a salt (A), the greenish yellow gas liberated as salt (A) is:

When $$MnO_2$$ and $$H_2SO_4$$ are added to salt A, a greenish-yellow gas is liberated. Identify salt A.

Greenish-yellow gas is chlorine ($$Cl_2$$).

$$MnO_2$$ acts as an oxidizing agent in the presence of $$H_2SO_4$$. When a chloride salt is present:

$$MnO_2 + 2H_2SO_4 + 2Cl^- \rightarrow Mn^{2+} + 2SO_4^{2-} + 2H_2O + Cl_2 \uparrow$$

The chloride ions are oxidized to chlorine gas.

The salt must contain $$Cl^-$$ ions. Among the options: $$CaI_2$$ (iodide), $$NaBr$$ (bromide), $$KNO_3$$ (nitrate), $$NH_4Cl$$ (chloride).

Only $$NH_4Cl$$ contains chloride ions.

The correct answer is Option (4): $$NH_4Cl$$.