Issued as a cumulative or non-cumulative L/C, the former allows for unused credit amounts to rollover into subsequent periods while the latter maintains a fixed amount of credit available each period.
average atomic mass of magnesium is 24.3 g/mole so 24.3 X 1.56 X1021 / 6.02 X1023 = .063 grams.
Magnesium as the atomic number 12. This means that each magnesium has 12 protons. Because Mg2+ has a net charge of +2e, it has 10 electrons, as explained above. Magnesium atoms may have 12, 13 or 14 neutrons. You cannot guess that, you have to look it up in an isotope chart. The isotope chart will show that there are three stable isotopes of magnesium: Mg-24, Mg-25, and Mg-26. The number is the mass number. It is the total number of protons and neutrons in the atom.