The oxidation number of nitrosyl fluoride (NOF) can be determined as follows:

1. Assign the oxidation number of fluorine (-1) to its atom.

2. Let "x" be the oxidation number of nitrogen.

3. The overall charge of the molecule is neutral; therefore, the sum of the oxidation numbers must be zero. This can be expressed as:

(1 x -1) + x = 0

4. Solving for "x," we get:

x = +1

Therefore, the oxidation number of nitrogen in nitrosyl fluoride is +1.