Hydrogen sulphide is useful as a reagent in the laboratory to detect the metal (basic) cations.

Ans.

1. Hydrogen sulphide reacts with salts of a number of metals forming the corresponding metal sulphides.
2. These sulphides vary in colour, depending upon the metal present, and are insoluble in water.
3. From the colour of their precipitate, the metal cations can be conveniently detected.
4. Hence, Hydrogen sulphide is useful as a reagent in the laboratory to detect the metal cations.