In dinitrogen trioxide (N2O3), the oxidation number of nitrogen (N) can be determined as follows:

Let x be the oxidation number of nitrogen. Since oxygen (O) generally has an oxidation number of -2 in most compounds, we can set up the equation:

2x + 3(-2) = 0

Simplifying the equation:

2x - 6 = 0

2x = 6

x = 6/2

x = 3

Therefore, the oxidation number for nitrogen in dinitrogen trioxide is +3.