The number of protons plus the number of neutrons equals the
atomic number
atomic mass
atomic weight
atomic neutrality

It equals the atomic mass. 

Molarity is moles of solute over liters of solution. idk if that is what you are talking about, but you can convert moles of solute to grams of solute using dimensional analyzes by using molar mass found on the periodic table.

Oxygen= 88ghydrogen= 12g