HNO2 is a neutral molecule, so the sum of the oxidation numbers of all atoms in the molecule must be zero.

Here's how to determine the oxidation number of each atom in HNO2:

* Oxygen (O): Oxygen usually has an oxidation number of -2. In HNO2, there are two oxygen atoms, so their total contribution is -4.

* Hydrogen (H): Hydrogen usually has an oxidation number of +1.

* Nitrogen (N): This is the unknown.

Let 'x' represent the oxidation number of nitrogen.

Now, we can set up the equation:

(+1) + (x) + (-4) = 0

Solving for x:

x - 3 = 0

x = +3

Therefore, the oxidation number of nitrogen (N) in HNO2 is +3.