Question

How do I write a balanced half-reaction describing the reduction of gaseous dioxygen to aqueous oxide anions?

Answer 1

oxide is O^2- so 
O2(g) + 4e- → 2O^2-(aq)

Answer 2

Answer:

Balanced half-reaction: $\frac{1}{2}O_{2}(g)+2e^{-}\rightarrow O^{2-}(aq.)$

Explanation:

Formula of dioxygen : $O_{2}$

Formula of oxide ion: $O^{2-}$

First balance oxygen atoms: $\frac{1}{2}O_{2}\rightarrow O^{2-}$

Then balance charge: $\frac{1}{2}O_{2}+2e^{-}\rightarrow O^{2-}$

Then mention physical state of all species to get balanced half- reaction:

               $\frac{1}{2}O_{2}(g)+2e^{-}\rightarrow O^{2-}(aq.)$