Textbook Problem

For each of the following oxidation-reduction reactions, identify which element is oxidized and which is reduced.

a. $\text{Mg}\left(\text{s}\right)+{\text{Br}}_{\text{2}}\left(\text{l}\right)\to {\text{MgBr}}_{\text{2}}\left(\text{s}\right)$   b. $\text{2Na}\left(\text{s}\right)+\text{S}\left(s\right)\to {\text{Na}}_2\text{S}\left(\text{s}\right)$   c. ${\text{CO}}_{\text{2}}\left(\text{g}\right)+{\text{H}}_{\text{2}}\left(\text{g}\right)\to \text{CO}\left(\text{g}\right)+{\text{H}}_{\text{2}}\text{O}\left(\text{g}\right)$   d. $\text{6K}\left(\text{s}\right)+\text{N2}\left(\text{g}\right)\to {\text{2K}}_{\text{3}}\text{N}\left(\text{s}\right)$