average atomic mass of an element=Atomic mass isotope₁ percent abundance isotope₁ + Atomic mass isotope₂ percent abundance isotope₂+Atomic mass isotope₃ percent abundance isotope₃....
average atomic mass=39.96 u0.9959+37.96 u0.00065+
35.97 u0.00366≈39.95 u
Answer: the average atomic mass of this element is 39.95 u
