Answer:
126.86
Explanation:
Iodine-127 (80%)
Iodine-126 (17%)
Iodine-128 (3%)
For a mixture of isotopes, the average atomic mass is obtained by summing the multiplication of the atomic mass and percentage composition of the individual isotopes. This is given as;
Average Atomic Mass = ( 80 / 100 * 127) + (17 / 100 * 126) + (3 / 100 * 128)
Average Atomic Mass = 0.8 * 127 + 0.12 * 126 + 0.03 * 128
Average Atomic Mass = 101.6 + 21.42 + 3.84 = 126.86
