Question

Calculate the reported average elemental atomic mass of $Mg$, if the naturally occurring isomers are ${}^{24}Mg,{}^{25}Mg,and{}^{26}Mg$. Their masses and abundance are as follows:
$$\begin{array}{ccc}\text{Isotope}& \text{Atomic Mass}& \text{Isotopic Abudance}\\ {}^{24}Mg& 23.98504& 78.70\%\\ {}^{25}Mg& 24.98584& 10.13\%\\ {}^{26}Mg& 25.98259& 11.17\%\end{array}$$

• A. 24.65 amu
• B. 24.31 amu
• C. 24.82 amu
• D. 24.90 amu

Answer 1

The correct option is B 24.31 amu

The average elemental atomic mass of $Mg$ will be
$=23.98504\times 0.787+24.98584\times 0.1013+25.98259\times 0.1117$
$=24.309$ amu