An element has two isotopes, X and Y, with mass numbers of 52.0 and 53.0 respectively. The relative atomic mass is 52.8. The percentage abundance of the two isotopes is Select one: a. X - 20% Y - 80% b. X - 25% Y - 75% c. X - 80% Y - 20% d. X - 75% Y - 25% e. X - 50% Y - 50%