Question

The activity of a radioactive element decreases to one-third of the original activity $A_0$ in a period of $9$years. After a further lapse of $9$years, its activity will be

• A. $A_0$
• B. $\frac{2}{3}{A}_0$
• C. $\frac{A_0}{9}$
• D. $\frac{A_0}{6}$

Answer 1

The correct option is C $\frac{A_0}{9}$

After a further period of $9$ years (a total of $18$), the activity should further decrease by a third.
Meaning, Activity $=\frac{1}{3}\times \frac{A_0}{3}$

Hence, activity becomes $\frac{A_0}{9}$