Calculating Oxidation State of Nitrogen in 2NO + O2 -> 2NO2

[dramadeur]

2NO + O₂ -> 2NO₂
"Oxidation of NO"

So a reactant - 2NO doesn't seem to lose an electron, it only gains an additional oxygen atom. So, I guess, oxidation is also gain of an oxygen? ...

 

[Bystander]

2Na + F₂ → 2NaF

Is this an oxidation?

 

[Borek]

NO doesn't seem to lose an electron

Do you know what oxidation state/oxidation number is? Can you calculate it for N?