Which of the following species is basic and reducing ?

The sulfite ion ${\mathrm{SO}}_3^{2-}$ can act as a basic and reducing species in certain chemical reactions.

Basic Properties:

The sulfite ion ${\mathrm{SO}}_3^{2-}$ can act as a base by accepting a proton (H⁺) to form the bisulfite ion (${\mathrm{HSO}}_3^{1-}$). For example, in an aqueous solution, the sulfite ion reacts with water to form the bisulfite ion and hydroxide ion:

${\mathrm{SO}}_3^{2-}$ + H₂O ⇌ ${\mathrm{HSO}}_3^{1-}$+ OH^-

The hydroxide ion produced in this reaction makes the solution basic.

Reducing Properties:

The sulfite ion can also act as a reducing agent by donating electrons to oxidizing agents. For example, in an acidic solution, the sulfite ion reacts with iodine (I₂) to form the iodide ion (I^-) and the sulfate ion ${\mathrm{SO}}_4^{2-}$:

${\mathrm{SO}}_3^{2-}$ + I₂ + 2H₂O → 2I^- + ${\mathrm{SO}}_4^{2-}$ + 4H⁺

In this reaction, the sulfite ion is oxidized to the sulfate ion, while the iodine is reduced to iodide ion. Therefore, the sulfite ion acts as a reducing agent.

Overall, the sulfite ion can exhibit both basic and reducing properties, depending on the reaction conditions and the nature of the reactants.