Question

Which of the following describes how the weighted average atomic mass of an element having two isotopes is determined?

(mass of isotope A + mass of isotope B)/ 2
(mass of isotope A + mass of isotope B) x (% abundance of isotope A + % abundance of isotope B)
(mass of isotope A) x (% abundance of isotope A) + (mass of isotope B) x (% abundance of isotope B)
2(mass of isotope A + mass of isotope B) + (% abundance of isotope A + % abundance of isotope B) / 2