The volume occupied by 345.2 g of Cl2 at STP is calculated as below
find the moles of Cl2 used
moles =mass/molar mass
molar mass of Cl2=35.5 x2= 71g/mol
moles= 345.2 g/ 71 g/mol =4.86 moles
at STP 1 mole= 22.4 liters
what about 4.86 moles
by cross multiplication
4.86moles/1mole x22.4 liters =108.86 liters of Cl2