Question

what happen when hydrogen gas is added to copper oxide?

Answer 1

Copper(II) oxide, CuO, will be converted to metallic copper when it is heated with hydrogen.

CuO + H2 = Cu + H2O

This reaction is a typical redox reaction (oxidation-reduction).

Answer 2

I believe it will be converted to metallic copper.

metallic copper is where you get your paint or spray paint from.

Hope this helped :)
Have a great day