Dear Rabnik ,
Crabon has four electron in valence shell and in carbon dioxide it uses its all four electron in forming bond with oxygen. So, carbon molecule can,t form more bonds hence it is less reactive..
While in sulphur it can form maximum 8 bonds and in SO2 it forms only four bond and it can still form bonds with other element to produce toxic thing ..
And in nitrogen it can form max. 5 bond , in NO2 it forms 4 bond it has one unpaired electron left and can form bond with some other element ..
Hope this will help you ...
Thanks and Regards
Adarsh