Question

The relative atomic mass of naturally occurring chlorine is not a whole number. What is the reason for this ?

• A. Chlorine atoms can have different number of neutrons
• B. Naturally occurring chlorine cannot be obtained pure
• C. Chlorine is unstable
• D. The mass of the electrons has been included

Answer 1

The correct option is A Chlorine atoms can have different number of neutrons

The relative atomic mass of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance.

Chlorine has two isotopes available in Nature.

One has At.mass = 35 which forms roughly $75\%$ of the naturally available Chlorine.

Another has At.mass = 37 which forms roughly $25\%$ of the naturally available Chlorine.

So they have fractional atomic mass.

Hence, the correct option is $\text{A}$