a
Moment of inertia in case $(i)$ is $I _{1}$
Moment of inertia in case $(ii)$ is $I_{2}$
$I_{1}=2 M R^{2}$
$I _{2}=\frac{3}{2} MR ^{2}$
$T _{1}=2 \pi \sqrt{\frac{ I _{1}}{ Mgd }} ; T _{2}=2 \pi \sqrt{\frac{ I _{2}}{ Mgd }}$
$\frac{ T _{1}}{ T _{2}}=\sqrt{\frac{ I _{1}}{ I _{2}}}=\sqrt{\frac{2 MR ^{2}}{\frac{3}{2} MR ^{2}}}=\frac{2}{\sqrt{3}}$
