Aqueous solution of `H_(2)S` contains `H_(2)S, HS^(-),S^(2-),H_(3)O^(+),OH^(-)` and `H_(2)O` in varying concentrations. Which of these species can act only as a base? Which can act only as an acid? Which can act both as an acid and as a base?

Explanation

a. `S^(2-)` can act only as a base. It canot act as acid because it cannot give `H^(+)` ions.
b. `H_(2)S` and `H_(3)O^(+)` can act only as acids.
c. `HS^(-),OH^(-)` and `H_(2)O` can act both acids and bases as they can give `H^(+)` ions and can accept `H^(+)` ions.