Question

Naturally-occurring chlorine (Cl) consists of
two isotopes; Cl-35 and Cl-37 and has an
atomic mass of 35.453. Which of the following
is a correct statement about which isotope is
the most abundant?

1. Cl-35 must be more abundant because
chlorine usually has 17 protons.
2. Cl-37 must be more abundant because
chlorine naturally has 7 electrons in its outer
shell.
3. Cl-35 must be more abundant because the
atomic mass of chlorine is closer to 35 than to
37.
4. Cl-37 must be more abundant because it
is larger and thus more stable.

Answer 1

Number 3. The listed atomic mass of an element is the average of the atomic masses of it's isotopes relative to their abundance, so it'll be closer to the more abundant isotope.

Answer 2

Thank you!!

Answer 3

You're welcome!