WAEC - Chemistry (2014 - No. 10)
The relative atomic mass of chlorine is not a whole number because
it is the weighted average mass of all its various isotopes
it is the average mass of all the isotopes of the element
the element has strong oxidizing ability
the atom contains a higher number of neutrons than protons
Explication
Chlorine is a mixture of two isotopes with different abundances. Its relative atomic mass is the mean or average of the isotopic masses.