First, we have to remember what a mass percentage means (in this particular case):
It is the amount of each element in a compound, and it is calculated as follows:
[tex]\%\text{ m/m = }\frac{mass\text{ of the element}}{mass\text{ of the compound}}*100\text{ }[/tex]The addition of the different mass percentages is equal to 100%.
In this case, we have the percentage of one of the elements of the compound, we can make the respective subtraction:
[tex]\%I\text{ = 100 - 13.6 = 86.4 \%}[/tex]Then, the answer is that the iodine mass percentage is 86.4%
