oxidizing agent and the reducing agent on the reactant side?

Cr₂O₃ is the oxidizing agent. This is because it is reduced as the oxidation number of Cr decrease from +3 (in Cr₂O₃) to 0 (in Cr).

CO is the reducing agent. This is because it is oxidized as the oxidation number of C increase from +2 (in CO) to +4 (in CO₂).

The oxidizing agent is the substance that gets reduced, so Cr2O3.
The reducing agent is the substance that gets oxidized, so CO.