Which Lassaigne`s extract $\left(N{a}_{2}S\right)$ is acidified with acetic acid and then lead acetate solution is added to it, the colour of the precipitate is

The sodium fusion extract is acidified with acetic acid and lead acetate solution is added. A black precipitate of lead sulphide indicates the presence of sulphur.

$\begin{array}{r}{\mathrm{Na}}_2\mathrm{S}+{\left({\mathrm{CH}}_3\mathrm{COO}\right)}_2\mathrm{Pb}⟶\\ \mathrm{PbS}\downarrow +2{\mathrm{CH}}_3\mathrm{COONa}\end{array}$