Question

 A hypothetical element X is found to have an atomic mass of 37.45 amu. Element X has only  two isotopes, X-37 and X-38. The X-37 isotope has a fractional abundance of 0.7721 and an  isotopic mass of 37.24. What is the isotopic mass of the other isotope? 

Answer 1

Ar= Ar₃₇* $\omega$₃₇ + Ar₃₈*$\omega$₃₈

37.45 = 0.7721* 37.24 + (1-0.7721)* X-38 $\implies$ X-38 = 38.16