The Lassaigne's extract is boiled with conc. $$\mathrm{HNO_3}$$ while testing for halogens. By doing so it

In Lassaigne's test for halogens, the sodium extract may also contain $\mathrm{Na_2S}$ and $\mathrm{NaCN}$. These interfere with the silver nitrate test because they can form silver sulfide or silver cyanide. Boiling the extract with concentrated $\mathrm{HNO_3}$ destroys these interfering ions by decomposing $\mathrm{Na_2S}$ and $\mathrm{NaCN}$. Therefore the correct option is the one stating this role.