A precipitate is fused on charcoal with $\mathrm{Na_2CO_3}$, extracted with water, treated with dil. $\mathrm{H_2SO_4}$ and $\mathrm{Na_2SO_3}$ + $\mathrm{BaCl_2}$ giving white precipitate; on heating the solution gas G evolves. Gas G will show which property?