Question

How much volume in liters will 100.0 g of oxygen occupy at 100 0C and 100 atm pressure?

Answer 1

Calculate the number of moles of O2 in 100.0 g using

Number of moles = mass/mass of one mole

this then gives you n in

PV=nRT

Answer 2

You find n from the mass of oxygen (O2)
n = (100.0 g of O2) / (1 mol O2 /32.00 g O2) =3.1 mol of O2
1 mol of any gas at STP has a volume of 22.4 L
1 mole of O2 = 32.0 g of O2 1 mole of O2 = 22.4 L of O2
100.0 g of O2 / 32.00 g of O2 = 3.1 mol of O2
3.1 mol of O2 * 22.4 L/ mol = 69.4 L of O2

Answer 3

But note that 100 C and 100 atm are not STP conditions.