d
In \(t_{1}\) time energy becomes half so charge will become \(\frac{1}{\sqrt{2}}\) time

\(q = Q _{0} e ^{\frac{ T _{1}}{ RC }}=\frac{ Q _{0}}{\sqrt{2}}\)

and \(q = Q _{0} e ^{\frac{ t _{1}}{ RC }}=\frac{ Q _{0}}{8}=\left(\frac{ Q _{0}}{\sqrt{2}}\right)^{6}\)

\(t _{2}=6 t _{1}\)

\(\frac{ t _{1}}{ t _{2}}=\frac{1}{6}\)