So chloroform is CHCl3 so the first thing we need to do is find out what the mass in amu of one atom of chloroform:
12.01amu(C)+1.008amu(H)+3*35.45amu(Cl3)=119.368amu
Then we find the amu of the Cl in the molecule which is 3*35.45amu=106.35amu
Then to find the percent by mass we take the mass of the 3 Cl divide it by the total mass of the molecule and multiply by 100.
so 106.35/119.368=0.89094 and 0.89094*100=89.094%
so the percent by mass of each chloroform molecule that is composed of chlorine is 89.094%!
I hope this helps!
