If all gases exist in a 2 atom combination, and they form covalent
bond.  How could you form a molecule of nitrogen?

H20 abov 100 degrees C is a gas and it's 3 atoms each. Have i missed something?

Not all gases exist in a 2-atom combination. However, most elements
that are gaseous at room temperature do form such molecules (an
obvious exception being the noble gases).

As for nitrogen, it just does it in the usual way. Since nitrogen has
five electrons in its outer shell, it needs an extra three to reach
eight. So a molecule of nitrogen has a triple covalent bond. The
electron dot diagram looks something like this:

   .   .,   ,
   . N ., N ,
       .,   

(well, it's the best I can do in plain text).

I agree with the aforementioned comments.  Not all gases consist of
two atoms each.  Carbon dioxide (C02) has three atoms.  The noble
gases such as helium and neon consist of a single atom.  There are a
number of exceptions to the two atom combination.

I want to thank you all for your help.  I was trying to help my
brother with his homework.

That was the actual question that he had to answer.

Have a Blessed Evening.