Answer:63.9%
Explanation: The percentage composition of chlorine in CaCl2 is derived as follows:
The molecular mass of the entire compound is:
Ca = 40.078 × 1 = 40.078
Cl2 = 35.4527 × 2 = 70.9054
40.078 + 70.9054 = 110.9834 (110.983 rounded)
The atomic mass of each element (or its multiple) is divided by the molecular mass of the compound:
Ca = 40.078 ÷ 110.983 = 0.361
Cl2 = 70.9054 ÷ 110.983 = 0.639
Multiplying each by 100 will turn these into percents. Therefore, the percentage composition of chlorine is 63.9%.