Shoreboy's answer does not make sense, it is because carbon has the ability to covalently bond with itself to form a macromolecular substance so it has strong covalent bonds for inter-molecular forces. Whereas nitrogen can only for Van der Waal inter-molecular forces which are much weaker and therefore require less energy to break, because these bonds are weaker lower temperatures have enough energy to break them and change the substances state to solid or gas.
...and if you do your own homework you will find the answer. Now that is has been 2 months I'll tell you...
While they are both in the 'non-metals' group the fact that Nitrogen has an odd number of electrons in it's outer shell (the P shell for both Carbon and Nitrogen) means that it is far easier for it to turn from solid to liquid to gaseous states. Which in turn means they happen at a lower 'temperature'. That works pretty much across the board in the periodic table. The 'balanced' atomic structures are the most stable requiring the most energy to change. The other primary factor is the 'shape' of the atomic structure... Hexagonal, cubic, Monoclinic, etc. basically the simpler the shape the lower the 'temperature' necessary to melt/boil.
Is it? What in the blue blazes have I been doing this whole time then?