Final answer:
The atomic weight of magnesium is not 12 amu. It is approximately 24.31 amu due to the presence of different isotopes.
Step-by-step explanation:
The statement is false. The atomic weight of magnesium is not 12 amu. The atomic weight of an element represents the average mass of all the isotopes of that element, taking into account the abundance of each isotope. For magnesium, the atomic weight is approximately 24.31 amu. This is because magnesium has several isotopes, with mass numbers ranging from 23 to 26.