First, we need to balance the equation by ensuring that the number of atoms of each element is the same on both sides of the reaction.
The half-reaction given is OH‾(aq) ⟶ O2(g)
To balance the oxygen atoms, we need to add a coefficient of 2 in front of OH‾ on the left side: 2OH‾(aq) ⟶ O2(g)
Next, we balance the hydrogen atoms. Since there are no hydrogen atoms on the left side, we add 2H⁺(aq) on the right side: 2OH‾(aq) ⟶ O2(g) + 2H⁺(aq)
Now, we balance the charge by adding electrons. Since each OH‾ ion has a charge of -1 and there are 2 OH‾ ions on the left side, the total charge is -2. To balance this, we add 4e⁻ on the left side: 2OH‾(aq) + 4e⁻ ⟶ O2(g) + 2H⁺(aq)
Now the equation is balanced.
Regarding whether it is an oxidation or reduction:
In this reaction, OH‾ is being converted to O2. Since oxygen is being gained, this is a reduction reaction.
So, the correct balanced half-reaction is: 2OH‾(aq) + 4e⁻ ⟶ O2(g) + 2H⁺(aq) (reduction)