Final answer:
The statement that is NOT true about molar mass is option A: The molar mass is 12 g for magnesium, because the actual molar mass of magnesium is approximately 24.31 g/mol.
Step-by-step explanation:
The question posed is regarding which statement is NOT true about molar mass. Let's examine the provided options: A: The molar mass is 12 g for magnesium. This statement is incorrect; the molar mass of magnesium is approximately 24.31 g/mol, not 12 g/mol. B: The molar mass is the mass of one mole of atoms. This statement is correct as molar mass represents the mass in grams of 1 mole of atoms for an element. C: The molar mass is found by checking the periodic table. This statement is correct, as the atomic weight listed on the periodic table is used to calculate the molar mass of an element. D: The molar mass is the number of grams of an element that is numerically equal to the mass in amu. This statement is correct; each element's molar mass in grams per mole is numerically equivalent to its atomic mass in atomic mass units (amu).
Therefore, the answer to the question, "Which of the following is NOT true about molar mass?" is option A: The molar mass is 12 g for magnesium.