Calculate the number of oxygen atoms in 15.0g of calcium nitrate

1 mol Ca (NO3) 2 has 6 O atoms and the mass of Ca (NO3) 2 is 164 g/mol.

1 mol has 164 g

X moles has 15g

X = 0.0915 mol Ca (NO3) 2

0.0915 x (6 O / 1 mol Ca (NO3) 2) = 0.549 mol O atoms

0.549 mol O x (6.02 x 10^23) = 3.30 x 10^23 atoms of O