c
(c)Initially magnetic moment of system \({M_1} = \sqrt {{M^2} + {M^2}} = 2M\) and moment of inertia \({I_1} = I + I = 2I.\)

Finally when one of the magnet is removed then \({M_2} = M\) and \({I_2} = I\)

So \(T = 2\pi \sqrt {\frac{I}{{M\;{B_H}}}} \) \(\frac{{{T_1}}}{{{T_2}}} = \sqrt {\frac{{{I_1}}}{{{I_2}}} \times \frac{{{M_2}}}{{{M_1}}}} = \sqrt {\frac{{2I}}{I} \times \frac{M}{{\sqrt 2 M}}} \)

\( \Rightarrow {T_2} = \frac{{{2^{5/4}}}}{{{2^{1/4}}}} = 2\;\sec .\)