The atomic masses of any two elements contain the same number of

They contain of atoms

Explanation:

That's because atomic weights or masses of each atom of each element are proportional to each other, the same number of atoms of each element will give masses that are also proportional to each other. If you start with 20 oxygen atoms, you will need 40 hydrogen atoms to make the water and you will get 20 molecules of water.

i'm not sure

explanation:

i'll try whatever you got

increased stability in the completion of fluorine's outer shell.