Question

Solution A gives black ppt. with dil.HCl and H2S gas, which basic radical is present in given solution

Answer 1

Hg2+ because hg form ppt in acidic medium in presence of H2S

Answer 2

Answer: $Hg^{2+},Cu^{2+}\text{ and }Pb^{2+}$ are the basic radicals formed when they are reacted with dil. HCl and $H_2S$ gas to form black precipitate.

Explanation: Dilute HCl and $H_2S$ gas are the reagents used for the qualitative analysis of Group II-A cations.

Group II-A cations are mercury $(Hg^{2+})$, lead $(Pb^{2+})$, Bismuth $(Bi^{3+})$, Cadmium $(Cd^{2+})$ and copper $(Cu^{2+})$.

These cations when reacted with the reagent forms respective salts.

Only mercury, lead and copper forms black precipitate with the reagent.

In a salt, the cationic part is considered as a basic radical and the anionic part is considered as the acidic radical.

So, from the salts of Group II-A, basic radicals would be $Hg^{2+},Cu^{2+}\text{ and }Pb^{2+}$