The atomics number of nitrogen is 7. how many protons, neutrons, and electrons make up an atom of nitrogen-15?

The atomic number of H is 7, which means that contains 7 protons in its nucleus and 7 electrons revolving around it.

If you add up the protons and electrons gives you equal the mass of the atom that would be 14.0067 in periodic table. 

But most of the times is passed to the next term to omit decimals, that is 15.

257 grams h2o i think