How to calculate..
The question is a little unclear. I am answering it according to what I have understood for it.
In general, in a compound see the central atom. Draw its lewis structure.Check its bonding and then you can check whether is there any unpaired electron in it or not.
In NO2, the structure is:
See here N has 5 valence electrons, with 2 electrons it forms a double bond, 2 electrons it donates for sharing as a coordinate bond. So, it is left one electron. So, it is an odd electron speices.
If you want to ask for any other type do ask again.