Answer:
Oxygen Doesn't change
However, Li is oxidized (0 to +1), Na is reduced (+1 to 0)
Step-by-step explanation:
On reactant side, Oxygen has -2 oxidation charge because we know common oxidation states such as oxygen -2, hydrogen +1 etc.
So NaOH, O is -2, H is +1, so Na has to be +1 to equal total charge of compound
In product side, LiOH, again O has to be -2, H is +1, so Li +1 as well..
We see that oxygen oxidation state doesn't change. However, for Li it becomes oxidized going from 0 to +1 whereas, Na is reduced going from +1 to 0.