Question

Suppose the mass spectrum of a hypothetical monatomic element x contains a signal at mass number 13 and another of identical height at mass number 15.

How many isotopes are present and why
What's the fractional abundance of the isotopes.why?

Answer 1

For this case, Only 1 isotope would be present, i.e. the principal element with mass M=13 and then one isotope at mass M+2. We are assuming that the principal element is the one that is the lowest mass - by definition, an isotope is one where there are additional neutrons - hence the mass increases, but the proton count is the same.