[AussieKenDoll]

Molecular Ion peak has the highest m/z ratio, according to this mass spectrum ,Molecular Ion peak is the 216 or the 219?

[MOTOBALL]

The molecular ion is taken as that composed of the lowest atomic mass of each element.
Thus, 12C, 1H, 16O,14N, 35Cl, 32S etc
For “small” molecules, less than about 1000 amu, the mol. ion will usually be the most intense peak in the mol. ion cluster.
For chloro-benzophenone it is m/z 216.

Regards,
Motoball

[AussieKenDoll]

The molecular ion is taken as that composed of the lowest atomic mass of each element.
Thus, 12C, 1H, 16O,14N, 35Cl, 32S etc
For “small” molecules, less than about 1000 amu, the mol. ion will usually be the most intense peak in the mol. ion cluster.
For chloro-benzophenone it is m/z 216.

Regards,
Motoball

What are the 3 small peaks after 216 peak?

[Corribus]

What do you know about most atoms? Do you have exact masses of those peaks?

[AussieKenDoll]

I understand now that the molecular ion peak is the 216 and other small peaks after 216 are isotopic peaks!

[Corribus]

Correct. In theory, the relative intensities of the isotopic peaks can tell you something about the number of carbons in the molecule.

[Babcock_Hall]

Ken,

I would call your attention to the peak at 218.

[AussieKenDoll]

what is that peak 218? It is a isotope peak right?

[Babcock_Hall]

It is an isotope peak.  Why do you think it is larger than the peak at 217?

[AussieKenDoll]

may be peak at 217 could be branched and peak at 218 is not or less branched!

[AWK]

https://www.lfd.uci.edu/~gohlke/molmass/?q=C13H9ClO

[Babcock_Hall]

may be peak at 217 could be branched and peak at 218 is not or less branched!

I don't know what you mean by "branched."  In any case there is a simple explanation, as suggested by AWK.