680 g of sodium 24 was placed in a container to decay if there is now 85 g of sodium 24 left how long has the sodium been decaying

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 hours.

Initial amount of sodium-24 is

In hours,the quantity falls to

In another hours,the quantity falls to

In another hours,the quantity falls to

So,it takes hours for the quantity to become .