Answer
\[\underline{\text{152 amu}}\]
Work Step by Step
Calculate the abundance of Eu-153 as follows:
\[\begin{align}
& \text{Abundance of Eu-}153=\frac{100\,\text{percent}}{100\,\text{percent}+88\,\text{percent}}\times 100\,\text{percent} \\
& =53.19\,\text{percent}
\end{align}\]
Calculate the abundance of Eu-151 as follows:
\[\begin{align}
& \text{Abundance of Eu-}151=\frac{88\,\text{percent}}{100\,\text{percent}+88\,\text{percent}}\times 100\,\text{percent} \\
& =46.81\,\text{percent}
\end{align}\]
Calculate the Eu-153 fraction as follows:
\[\begin{align}
& \text{Fraction isotope Eu-}153=\frac{53.19}{100} \\
& =0.5319
\end{align}\]
Calculate the Eu-151 fraction as follows:
\[\begin{align}
& \text{Fraction isotope Eu-}151=\frac{46.81}{100} \\
& =0.4681
\end{align}\]
Calculate the atomic mass of the element as follows:
\[\begin{align}
& \text{Atomic mass}=\left( \text{fraction of Eu-}153\times \text{mass of Eu-}153 \right)+ \\
& \left( \text{fraction of Eu-}151\times \text{mass of Eu-}151 \right) \\
& =\left( 0.5319\times 153\text{ amu} \right)+\left( 0.4681\times 151\text{ amu} \right) \\
& =81.38\text{ amu}+70.68\text{ amu} \\
& =152.06\text{ amu}\,\,\approx \,\,152\text{ amu}\,
\end{align}\]
The atomic mass of europium is \[\underline{\text{152 amu}}\].
