## Chemistry: An Atoms-Focused Approach

(a) $^{20}$Ne (b) $^{35}$Cl (c) $^{132}$Xe
(a) To determine which of the two naturally occurring isotopes of neon is more abundant, we look at the average atomic mass of neon, which is 20.180 amu from our periodic table. Because 20.180 amu is closer to 20 than to 22, that means $^{20}$Ne is more abundant than $^{22}$Ne. (b) To determine which of the two naturally occurring isotopes of chlorine is more abundant, we look at the average atomic mass of chlorine, which is 35.453 amu from our periodic table. Because 35.453 amu is closer to 35 than to 37, that means $^{35}$Cl is more abundant than $^{37}$Cl. (c) To determine which of the two naturally occurring isotopes of xenon is more abundant, we look at the average atomic mass of xenon, which is 131.29 amu from our periodic table. Because 131.29 amu is closer to 132 than to 134, that means $^{132}$Xe is more abundant than $^{134}$Xe.