The correct option is C a redox reaction
A redox reaction is the reaction in which both oxidation and reduction takes place.
Photosynthesis can be categorized as a redox reaction. Here, the water molecule is oxidized to release oxygen whereas carbon dioxide is reduced to form glucose.
Since both oxidation and reduction reactions take place in the process of photosynthesis, it cannot be classified as just an oxidation reaction or a reduction reaction. Hence, option (a) and (b) can be eliminated.