Which molecular formula is consistent with the following mass spectrum data? M⁺ ^. at m/z= 78, relative height=23.5%
(M+1) ⁺ ^. at m/z= 79, relative height=0.78%
(M+2) ⁺ ^. at m/z= 80, relative height=7.5%

Question

Quizplus · Accepted Answer

The mass spectrum data shows three peaks at m/z values of 78, 79, and 80 with relative heights of 23.5%, 0.78%, and 7.5%, respectively. These peaks indicate the presence of different isotopes of certain elements in the molecular formula. The molecular formula that matches the data must contain at least one element with isotopes that differ by 1 or 2 mass units. 
The only molecular formula that contains such elements is Choice B, which contains chlorine (Cl) with isotopes of mass 35 and 37. The two peaks at m/z 78 and 80 could represent the molecular ion and the ion with one chlorine-35 isotope, respectively, while the peak at m/z 79 could correspond to the ion with one chlorine-37 isotope. The relative heights of the peaks support this interpretation. 
None of the other choices contain appropriate elements or isotopes to match the mass spectrum data.

Which Molecular Formula Is Consistent with the Following Mass Spectrum