Chapter 5, Problem 4PE

Assign oxidation numbers to each atom in $\left(\text{a}\right){\text{ NiCl}}_{\text{2}}\text{, }\left(\text{b}\right){\text{ Mg}}_{\text{2}}{\text{TiO}}_{\text{4}}\text{, }\left(\text{c}\right){\text{ K}}_{\text{2}}{\text{Cr}}_{\text{2}}{\text{O}}_{\text{7}}\text{, }\left(\text{d}\right){\text{ H}}_{\text{3}}{\text{PO}}_{\text{4}}\text{, }\left(\text{e}\right)\text{ V}{\left({\text{C}}_{\text{2}}{\text{H}}_{\text{3}}{\text{O}}_{\text{2}}\right)}_{\text{3}}\text{. and }\left(\text{f}\right){\text{ NH}}_4^{+}\text{.}$