In a periodic table, the averge 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 `._12Mg^(24) (23.98504u)`, `._(12)Ng^(25) (24.98584)` and `._12Mg^(26) (25.98259 u)`. The natural abundance of `._12Mg^(24)` is `78.99%` by mass. Calculate the abundances of the other two isotopes.

Explanation

Let the abundance of `._(12)Mg^(25)` by mass be `x%`. Therefore, abundance of `._(12)Mg^(26)` by mass
`=(100-78.99-x)%=(21.01-x)%`
Now, average atomic mass of magnesium is :
`24.312=(23.98504xx78.99+24.98584x+25.98259(21.01-x))/100`
on solving, we get `x=9.303%` for `._(12)Mg^(25)` and for `._(12)Mg^(26), (21.01-x)=11.71%`