A compound containing C, N, S and Cl is fused with sodium. Before adding $AgNO X_{3}$ to the sodium extract for the chlorine test, the extract is acidified with dilute $HNO X_{3}$ and boiled. The purpose of boiling is to

Aoxidise $Cl X^{-}$ to $Cl X_{2}$ so that it can be detected
Bconvert $AgCl$ into the soluble $[Ag (NH X_{3}) X_{2}] X^{+}$
Cexpel $HCN$ and $H X_{2} S$ so that $CN X^{-}$ and $S X^{2 -}$ do not precipitate with $Ag X^{+}$
Dconvert $NaSCN$ into $NaCN$ and sulphur

Answer: C

CN X^{-}

and

S X^{2 -}

would give

AgCN

and

Ag X_{2} S

with

Ag X^{+}

and mask the white

AgCl

. Acidification converts them to volatile

HCN

and

H X_{2} S

, which are driven off on boiling, leaving

Cl X^{-}

in solution.