Answer:
1.38269 amu
Explanation:
Gadolinium-157 has 64 protons and 93 neutrons. Recall that mass defect his the difference between the calculated mass and the actual mass of the atom. This difference in calculated mass and actual mass exists because some mass is converted to the binding energy of the nucleus.
Mass of 64 protons= 64 × 1.007825 = 64.5008 amu
Mass of 93 neutrons= 93 × 1.008665 = 93.805845 amu
Mass of neutrons and protons= 64.5008 + 93.805845 = 158.306645 amu
Mass defect= 158.306645 - 156.92396 = 1.38269 amu
Therefore, mass's defect of gadolinium-157 is 1.38269 amu
