Carbon monoxide possesses both oxidising and reducing properties - why ?

Explanation

Oxidation state of carbon in carbon monoxide is +2. It stands in between its highest oxidation state (+4) and lowest oxidation state ( - 4) . As a result, in chemical reactions, the carbon atom in CO may increase its oxidation number from +2 to +4 or it may decrease its oxidation number from +2 to - 4 . When oxidation number increases, CO is oxidised and plays the role of a reducing agent. For example, at high temperature, CO reduces black CuO to red metallic Cu.
`overset(+2)(Cu)O+overset(+2)CO to overset(0)(Cu)+ overset(+4)(CO_2)`
On the other hand, in case of decrease in oxidation number of carbon, carbon monoxide undergoes reduction, i.e., it acts as an oxidising agent. For instance, in the following reaction, carbon monoxide oxidises hydrogen producing water and itself gets reduced to methane.
`overset(+2)CO+3overset(0)H_2underset(250-300^@C)overset(Ni)to overset(-4)Cu+overset(+1)H_2O`