6 Atoms!
Mg = 1 atom.
O = 4 atoms.
A = 1 atom.
Though the ratio of any two atom's masses was the same on either scale, it was horribly confusing, so in 1961, a compromise was reached. Instead of using either Hydrogen, or Oxygen as the standard, the isotope of Carbon<span> with 6 </span>protons<span> and 6 neutrons in its nucleus (</span>Carbon-12<span>) was given a mass of exactly 12.</span>
