You'd need 87.5 g of chlorine gas.
The balanced chemical equation for this reaction looks like this
Chlorine and phosphorus trichloride have a
So, in order to produce 0.823 moles of phosphorus trichloride, the reaction needs
To get the mass in grams that would contain this many moles, use chlorine gas' molar mass
Rounded to three sig figs, the number of sig figs you gave for the number of moles of phosphorus trichloride produced, the answer will be