Question

2.5g of magnesium is how many moles?
How do i set it up? Help would be awesome thanks.

Answer 1

mols = grams/atomic mass

Answer 2

From the periodic table, you get the atomic mass of Mg, which is 24.31. Atomic mass is grams/mole, by dimensional analysis:

(2.5g)/(24.31g/mol)=0.1028 moles of Magnesium as the grams units cancel out.

*This answer does not have proper significant figures.