In a periodic table the average atomic mass of magnesium is given as $24.312\;u$ The average value is based on their relative natural abundance on earth. The three isotopes and their masses are $_{12} Mg^{24}(23.98504\;u)$, $_{12} Mg^{25}(24.98584\;u)$ and $_{12} Mg^{24}$ is $78.99\%$ by mass. Calculate the abundances of the other two isotopes.

Question

$\begin{array}{1 1} _{12}Mg^{25}=9.303\%\;and\;_{12}Mg^{26}=11.71\% \\ _{12}Mg^{25}=11.71\%\;and\;_{12}Mg^{26}=9.303\% \\ _{12}Mg^{25}=93.03\%\;and\;_{12}Mg^{26}=1.171\%\\ _{12}Mg^{25}=1.171\%\;and\;_{12}Mg^{26}=93.03\% \end{array} $