Answer:
Chlorine --> 89%
Explanation:
Step 1) Add each element's amu up to get the total mass of the compound.
12.011+1.008+3(35.453) = 119.378.
Step 2) Divide the total mass of chlorine by the total mass of the compound.
3(35.453) = 106.359
106.359/119.378 = 0.8909430548.
Step 3) Now multiply by 100 to get the percentage.
0.8909430548*100 = 89.09430548%
Step 4) Estimate and submit your answer
89.09430548% estimates to 89%
