NO3 oxidation?

Question

I know N is +5
and O is -2

But why? I mean, there are 3 O's, so that'd be -6 right? And why is N +5?

Answer 1

Nitrate is an anion, NO3- , not neutral NO3.

So if you give the oxygens 6 electrons between them, one comes from the charge and only 5 from the nitrogen.

You always need to take into account the charge on an ion. For example, the ammonium ion is NH4+, so the oxidation numbers have to add up to +1. Each hydrogen is assigned +1, so the nitrogen in this ion is -3.