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 `_12Mg^(24) (23.98504u)`, `._(12)Mg^(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, an abundance of
`12_Mg^26` by mass=`(100−78.99−x)%`

=`(21.01−x)%`

Now, the average atomic mass of Mg is `24.312`=`23.98504`×`(78.99/100)`+`24.98584`× `(x/100)`+`25.98259`×`(21.01−x)`/100


⟹`x=9.303%` for `12Mg`
25