The Lassaigne's extract is boiled with conc. $HNO_3$ while tessting for halogens. By doing so it :

Question

( A ) increases the concentration of $NO_3^-$ ions
( B ) increases the solubility product of $AgCl$
( C ) helps in the precipitation of $AgCl$
( D ) decomposes $Na_2S$ and $NaCN$, if formed