Can you provide an example in which copper(II) oxide acts as an oxidizing agent?

A classic example of a redox reaction in which copper(II) oxide acts as an oxidizing agent involves the oxidation of hydrogen gas to water.

#"CuO"_ ((s)) + "H"_ (2(g)) -> "Cu"_ ((s)) + "H"_ 2"O"_ ((l))#

The idea here is that copper(II) oxide will oxidize hydrogen gas to water while being reduced to copper metal in the process.

If you assign oxidation numbers to all the atoms that take part in the reaction, you will see that copper's oxidation number decreases from #color(blue)(+2)# on the reactants' side to #color(blue)(0)# on the products' side #-># copper is being reduced.

On the other hand, the oxidation number of hydrogen increases from #color(blue)(0)# on the reactants' side to #color(blue)(+2)# on the products' side #-># hydrogen is being oxidized.

#stackrel(color(blue)(+2))("Cu") stackrel(color(blue)(-2))("O")_ ((s)) + stackrel(color(blue)(0))("H")_ (2(g)) -> stackrel(color(blue)(0))("Cu")_ ((s)) + stackrel(color(blue)(+2))("H")_ 2 stackrel(color(blue)(-2))("O")_ ((l))#

You can thus say that copper(II) oxide acts as an oxidizing agent because it oxidizes hydrogen gas to water.

Similarly, hydrogen gas acts as a reducing agent because it reduces copper(II) oxide to copper metal.