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.
A. Sketch the mass spectrum. Make sure each axis is properly labeled.
B. How many isotopes are present? Why?
C. What are the fractional abundances of the isotopes? Why?

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.
A. Sketch the mass spectrum. Make sure each axis is properly labeled.
B. How many isotopes are present? Why?
C. What are the fractional abundances of the isotopes? Why?

abb0t · Answer

1. Ur graph should have 2 vertical lines || , of equal height at mass 13 and 15. 

2. I believe that you should have ONE. because you have the mass, which in this case is 13 and the other 15, which clearly has the same height. So it must be the isotope. By defiition a isotope has the same number of protons, but different number of neutrons. 

3. to solve for fractional abundance, Let x = fraction of element: "I"-13 
then fraction of "I"-15 must be 1-x 
so you have: $\sf\color{red}{13}$x + ($\sf \color{red}{15}$)(1-x) = 13 
solve for x.