Question: how many atoms are present in 14u of nitrogen?
Answer: What is the number of atoms present in 14 u of N₂? Since the mass of one nitrogen atom is 14 u (unified atomic mass units), you can't have 14 u of N₂. (One N₂ molecule has a mass of 28 u.) 14 u of N₂ would involve 1/2 of an atom, which is an impossibility in chemistry.