An unknown element X has the following isotopes: 58X (68.00% abundant), 0X (26.00% abundant), 2X (6.00% abundant). What is the average atomic mass in amu of X? 56 26 26 26 Iron exists in nature as a mixture of predominantly three isotopes: 542Fe (53.94 amu), 5 Fe (55.93 amu), and 57 Fe (56.94 amu). If the most common isotope, 56 Fe, accounts for 91.75% of iron atoms, and the average atomic mass of iron is 55.85 amu, what is the percent abundance of the rarest of these three isotopes of iron? 26