Question

Indium consists of two isotopes, ${}_{49}{}^{113}In$and ${}_{49}{}^{115}In$. If the atomic mass for indium on the periodic table is $114.8$, are there more atoms of ${}_{49}{}^{113}In$or ${}_{49}{}^{115}In$in a sample of indium?

Short answer

There are more atoms of ${}_{49}{}^{115}In$in a sample of indium.

Step-by-step solution

Given Information

We are required to determine which indium isotope is more naturally occurring in nature. Here, we are given the atomic number and the atomic masses of the two isotopes of indium and we also have the average atomic mass of indium.

Explanation

We know that

The atomic mass of an element on the periodic table is used to find the most abundant isotope. The atomic mass of indium is $114.8$, as can be shown. Although no indium atom has that mass, it is the average mass of an indium sample.

When comparing the atomic masses of ${}_{49}{}^{113}In$and ${}_{49}{}^{115}In$, we can see that the atomic mass number on the periodic table is closer to that of ${}_{49}{}^{115}In$.

We can deduce that ${}_{49}{}^{115}In$is more plentiful.