[paul9797]

A certain mass spectrum shows three peaks.  The first is at m/z = 39.5 Daltons with a relative abundance of 100%, the second is at m/z = 40.0 Daltons with a relative abundance of 5.8%, and the third is at m/z = 40.5 Daltons, with a relative abundance of 0.1%.  What is the charge on the ion?  If the molecule is of the form CnHxOyNz, propose a plausible formula.   Any of n, x, y, or z may be zero.

I am having trouble finding the charge let alone the formula. Please help me!

[MOTOBALL]

Well, do any atoms ( or combination of atoms) have mass (atomic weight) = 39.5 ( or 11.5 or 55.5 or ...or..)?
And I mean individual isotopes, not average atomic weight.
m/z = 39.5 is just a mathematical equation.
So, if m = 39.5 x Z, what is Z to give a unit integer mass ?