The metal whose oxide can be reduced by common reducing agents:

Copper

Reason — Copper lies below hydrogen in the reactivity (activity) series, so its oxide is not very stable. Therefore, common chemical reducing agents such as carbon, carbon monoxide, or hydrogen can readily reduce copper(II) oxide to metallic copper, e.g.

CuO + H₂ → Cu + H₂O

In contrast, the oxides of sodium, aluminium and potassium are extremely stable because those metals are highly reactive and have a very strong affinity for oxygen. Their oxides can be reduced only by electrolysis and not by ordinary chemical reducing agents.