Answer:
[tex]5[/tex] mg parent isotope would be left after 2 million years
Explanation:
It is given that half life of parent isotope is equal to one million years.
Half life period indicates the number of years required by an isotope to reduce its quantity by half.
Amount of parent isotope left after first half life period i,e after [tex]1[/tex] million years
[tex]= \frac{20}{2} \\= 10[/tex]mg
Amount of parent isotope left after second half life period i,e after [tex]2[/tex] million years
[tex]= \frac{10}{2} \\= 5[/tex]mg
