Answer:
32.92 moles of Mg
Step-by-step explanation:
To convert grams to moles (Or vice versa) of any chemical compound we need to use the molar mass of the substance (That is, how many grams weighs 1 mole of the chemical).
The magnesium, Mg, has a molar mass of 24.305g/mol. That means in 800.0g of Mg you have:
800.0g * (1mol / 24.305g) =
32.92 moles of Mg