Chapter 14, Problem 2PP

Assign oxidation numbers to each element in the following formulas.

$\begin{array}{l}\left(\text{a}\right)\text{ Mg}\\ \left(\text{b}\right){\text{ Mn}}_{\text{2}}{\text{O}}_{\text{3}}\\ \left(\text{c}\right){\text{ Na}}_{\text{2}}{\text{SO}}_{\text{4}}\\ \left(\text{d}\right){\text{ Cr}}_{\text{2}}{\text{O}}_7^{2-}\end{array}$