The activity of a sample reduces from A0 to $\frac{A_0}{\sqrt 3}$ in one hour.   The activity after 3 hours more will be

$\frac{A_0}{3\sqrt 3}$ $\frac{A_0}{9}$ $\frac{A_0}{9\sqrt 3}$ $\frac{A_0}{27}$

$\frac{A_0}{3\sqrt 3}$

$A_1 = A_0 e^{-\lambda t}$ $\Rightarrow \frac{A_0}{\sqrt 3} = A_0 e^{-\lambda}$ .....(1) $ A' = A_0 e^{-3\lambda} = A_0 (\frac{1}{\sqrt 3})^3 = A_0 \frac{1}{3\sqrt 3}$