In NHO3, the oxidation number of nitrogen (N) is +5, hydrogen (H) is +1, and oxygen (O) is -2. To determine the oxidation number of nitrogen, we can use the following steps:

1. Assign the oxidation number of oxygen (-2) to each oxygen atom in the compound. There are three oxygen atoms, so the total contribution from oxygen is 3 * (-2) = -6.

2. Assign the oxidation number of hydrogen (+1) to each hydrogen atom in the compound. There is one hydrogen atom, so the contribution from hydrogen is 1 * (+1) = +1.

3. Let x be the oxidation number of nitrogen.

4. The sum of the oxidation numbers of all atoms in a neutral compound must be zero. Therefore, we can write:

```

x + (-6) + (+1) = 0

```

5. Solving for x, we get:

```

x = +5

```

Therefore, the oxidation number of nitrogen in NHO3 is +5.