The relative atomic mass of chlorine is not a whole number because

A.

it is the weighted average mass of all its various isotopes

B.

it is the average mass of all the isotopes of the element

C.

the element has strong oxidizing ability

D.

the atom contains a higher number of neutrons than protons

Correct answer is B

Chlorine is a mixture of two isotopes with different abundances. Its relative atomic mass is the mean or average of the isotopic masses.