b
The \(M I\) about the axis of rotation is not rotation is not constant as the perpendicular distance of the bead with the axis of rotation increases. Also since no external torque is acting, therefore,

\(\tau_{e x t}=\frac{d L}{d t}\)

\(\Rightarrow L=\mathrm{constt.}\)

\(I \omega=\mathrm{constt.}\)

since \(l\) increases \(\omega\) decreases.