At STP one mole of gas will occupy 22.4 liters. ( This is Avogardo's volume which will contain Avogardo's number of molecules
To find the number of moles divide 162 Liters the volume by the molar volume of 22.4 liters/mole
Now multiply the number of moles time the grams per mole for chlorine gas.
Chorine can form either a diatomic gas or at lower temperatures a complex of 8 chlorines. For this problem assume the more common diatomic gas. This molecule has two Chlorines.
2 moles x 35.4 grams/mole = 70.8 grams
Now multiply the grams/mole by the number of moles.
70.8 g/ moles x 7.23 moles = 512 grams
In most problems it is best to change to moles.