Which of the following can funtion as an oxidizing as well as a reducing agent ?

Options

A. `N_2O_5`
B. `H_2S`
C. `H_2SO_4`
D. `SO_2`

Answer

D

Explanation

A species can work both as an oxidizing agent and a reducing agent if the central atom is present in the intermediate oxidation state so that it can be oxidized (increase of oxidation number ), playing the role of a reducing agent, as well as reduced (decrease of oxidation number ), playing the role of an oxidizing agent.
For S, the lowest oxidation number is ` -2` and the highest oxidation number is ` +6`. In ` SO_2`, the ` O.N.` of S is ` +4` which is neither highest (i.e. , +6) nor lowest (i.e., -2) . Thus, it can act both as an oxidizing and a reducing agent.
In ` N_2O_5,N` atom has its highest ` O.N.`, thus, it functions only as an oxidizing agent. In ` H_2S, S` atom has its lowest ` O.N.`, thus, it functions only as a reducing agent. Similarly. ` H_2SO_4` can function only as an oxidizing agent as S gas its maximum oxidation number.
The terms oxidation number and oxidation state are used interchangeably. However, the term oxidation state is preferred when the atom in a given species undergoes a change of oxidation number.