Chlorine naturally exists as two isotopes, \(_{17}^{35}\textrm{Cl}\) (chlorine-35) and \(_{17}^{37}\textrm{Cl}\) (chlorine-37). The abundance of chlorine-35 is 75% ...

Relative atomic mass is an average mass, which takes into account all of the isotopes and their abundance. It is not always a whole number. However, on your data leaflet, apart from chlorine ...