Q. Explain about Hydrogen Sulphide?

Hydrogen sulphide is the only thermodynamically stable sulphane. It is a foul smelling and poisonous gas.

H₂S is prepared in the laboratory by treating FeS with dilute HCI in Kipp's apparatus. In aqueous solution H, S is a weak acid. At 293 K, it dissociates as shown below: 

You must have used H₂S in qualitative identification and separation of cations. This separation is based on selective precipitation of the sulphides in acidic and alkaline medium:  In the acidic medium, the ionisation of H₂S which is a weak acid, is further suppressed and the solubility product of sulphides of relatively less soluble cations of Group 11, namely.  Pb^2+, Hg²⁺, Bi³⁺, Cu²⁺ , Cd₂₊ . As^3+, Sb^3+, Sn⁺² is exceeded:

In Group IV, in the presence of ammonia, a higher concentration of S^2- ions is obtained leading to the precipitation of the more soluble sulphides of Zn, Mn, Ni and Co.