Respuesta :

1. Go to periodic table and find the atomic mass (top little number) of each element.
2. Multiply each atomic mass by the number of atoms in the formula.
3. Add up the results together. 
Beth1309
Chlorine has a mass number of 35.5 (you know this from looking at the periodic table).

As you are looking at Cl2 you have two chlorine atoms meaning to calculate the molar mass you do 35.5+35.5= 71 mol