The Lassaigne's extract is boiled with conc. $$\mathrm{HNO_3}$$ while testing for halogens. By doing so it
Aincreases the concentration of $$\mathrm{NO_3^-}$$ ions
Bdecomposes $$\mathrm{Na_2S}$$ and $$\mathrm{NaCN}$$, if formed
Chelps in the precipitation of $$\mathrm{AgCl}$$
Dincreases the solubility product of $$\mathrm{AgCl}$$
Answer & Solution
Correct answer: B. decomposes $$\mathrm{Na_2S}$$ and $$\mathrm{NaCN}$$, if formed
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.
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