Final answer:
The oxidation number for nitrogen is -3 in NH4 (ammonium), +4 in NO2, and 0 in molecular N2.
Step-by-step explanation:
To determine the oxidation number of nitrogen in different compounds, we apply the rules for oxidation states. For the compound NH4, which is commonly encountered as the ammonium ion (NH4+), nitrogen has an oxidation state of -3, because hydrogen generally has an oxidation state of +1 and the total charge of the ion is +1. When considering NO2, each oxygen has an oxidation number of -2, so the total oxidation state of oxygen in the molecule is -4. Given the molecule is neutral, and based on the reference statement, the nitrogen must have an oxidation number of +4 for the charges to balance. For molecular N2, nitrogen is in its most stable elemental form, and the oxidation number for an element in its pure form is always 0. Therefore, the oxidation numbers for nitrogen in NH4, NO2, and N2 are -3, +4, and 0, respectively.