Chapter 8.4, Problem 26PP

Identify each of the following as an oxidation or a reduction:

$\begin{array}{l}a.{\text{ O}}_{\text{2}}\left(g\right)+4e^{-}\to 2O^{2-}\left(aq\right)\\ \begin{array}{l}b.Ag\left(s\right)\to A{g}^{+}\left(aq\right)+e^{-}\hfill \\ c.F{e}^{3+}\left(aq\right)+e^{-}\to F{e}^{2+}\left(aq\right)\hfill \\ d.2B{r}^{-}\left(aq\right)\to B{r}_2\left(l\right)+2e^{-}\hfill \end{array}\end{array}$