Explanation:
The time taken for the radioactivity of a specified isotope to fall to half its original value is called half life of that radioactive material.
Half life of sodium-24 is [tex]14.9[/tex] hours.
Initial amount of sodium-24 is [tex]680g[/tex]
In [tex]14.9[/tex] hours,the quantity falls to [tex]\frac{680}{2}=340g[/tex]
In another [tex]14.9[/tex] hours,the quantity falls to [tex]\frac{340}{2}=170g[/tex]
In another [tex]14.9[/tex] hours,the quantity falls to [tex]\frac{170}{2}=85g[/tex]
So,it takes [tex]14.9+14.9+14.9=44.7[/tex] hours for the quantity to become [tex]85g[/tex].
