Marnett930 Marnett930 24-08-2014 Chemistry Answered Element X is found in two forms: 90.0% is an isotope that has a mass of 20.0, and 10.0% is an isotope that has a mass of 22.0. What is the atomic mass of element X? A. 20.0 B. 20.2 C. 20.8 D. 21.2 E. 21.8 Can anyone explain this one for me?