Time constant $\tau = \frac{2}{In(2)}$
$I = I_o e^{-t/\tau}$
$\begin{align*}\frac{I_1}{I_2} = \frac{e^{^{-2/(2/In2)}}}{e^{^{-6/(2/In2) }}} \end{align*}$
$\begin{align*}= \frac{e^{3In2}}{e^{In2}} = \frac{2^3}{2} = \frac{4}{1} \end{align*}$
Ans : (c) 4 : 1