Question

The oxidation numbers of nitrogen in NH4+, NO2, and NaNO3 are, respectively:

-3, +4, +5

+3, +5, +4

+3, +5, -4

-3, -4, +5

Answer 1

Hydrogen has a +1charge and the whole thing has a +1charge so
(N)+4(H)=+1
and plug in H you get
(N)+4(1)=1 which means N has a charge of -3
If you use that set up for the rest you should be able to figure them out if there is no overall charge you just set it equal to 0