Which of the following compound is added to the sodium extract before addition of silver nitrate for testing of halogens?

In the Lassaigne's test (sodium fusion test) for halogens, the sodium extract may contain sodium cyanide ($$NaCN$$) and sodium sulphide ($$Na_2S$$) along with sodium halides. Both $$CN^-$$ and $$S^{2-}$$ ions can interfere with the silver nitrate test because they form insoluble precipitates with $$Ag^+$$: $$AgCN$$ (white) and $$Ag_2S$$ (black).

To remove these interfering ions, the sodium extract is first boiled with dilute nitric acid ($$HNO_3$$) before adding silver nitrate. The nitric acid decomposes $$NaCN$$ and $$Na_2S$$: $$NaCN + HNO_3 \rightarrow NaNO_3 + HCN\uparrow$$ and $$Na_2S + 2HNO_3 \rightarrow 2NaNO_3 + H_2S\uparrow$$. The volatile $$HCN$$ and $$H_2S$$ escape, leaving only the halide ions to react with silver nitrate.

Therefore, the compound added to the sodium extract before addition of silver nitrate is nitric acid, which is option (1).