To solve this problem, we need to use the ideal gas law:
#PV=nRT#
#P# is pressure in atmospheres, #V# is volume in liters, #n# is moles, #R# is the universal gas constant, and #T# is the temperature in Kelvins.
First, we will need to convert each of the units.
#894color(white)(l)-:1000=0.894 color(white)(l)L#
#(772color(white)(l)mmHg)/1times(1color(white)(l)atm)/(760color(white)(l)mmHg)=1.02# atm
#28+273=301color(white)(l)K#
Now, plug the above values into the equation and solve for moles.
#(1.02)(0.894)=(n)(0.08206)(301)#
#n=((1.02)(0.894))/((0.08206)(301))=0.0369color(white)(l)molcolor(white)(l)ClF_3#
Finally convert moles of #ClF_3# to grams:
#(0.0369color(white)(l)molcolor(white)(l)ClF_3)/1times(92.448color(white)(l)gcolor(white)(l)ClF_3)/(1color(white)(l)molcolor(white)(l)ClF_3)=3.41color(white)(l)gcolor(white)(l)ClF_3#