Rules to Remember

* Oxygen's oxidation number is usually -2, except in peroxides (like H₂O₂) where it's -1.

* The sum of the oxidation numbers in a neutral molecule is 0.

Applying the Rules

1. Let x be the oxidation number of N.

2. Oxygen has an oxidation number of -2. Since there are two oxygen atoms, their total contribution is -4.

3. The overall charge of NO₂ is 0.

4. Set up the equation: x + (-4) = 0

5. Solve for x: x = +4

Therefore, the oxidation number of nitrogen (N) in NO₂ is +4.