Question

What is the oxidation number of nitrogen in `N_2O_5`?

Answer 1

`+5`

Explanation:

Two things come in handy here

• for a neutral compound, the sum of the oxidation numbers of all constituent atoms must be equal to zero
• the oxidation number of oxygen is usually equal to `-2`

This means that if you take `?` to be the oxidation number of nitrogen in dinitrogen pentoxide, `"N"_color(blue)(2)"O"_color(red)(5)`, you can say that

`color(blue)(2) xx ? + color(red)(5) xx (-2) = 0`

All you have to do now is solve for `?` to find

`color(blue)(2) xx ? = +10 implies ? = (+10)/2 = +5`

And there you have it, nitrogen has a `+5` oxidation number in dinitrogen pentoxide.