The cross-sections of two solid bars made of the same material are shown in the figure. The
square cross-section in the figure. The square cross-section has flexural (bending) rigidity$I_{1}$ while
the circular cross-section has flexural rigidity$I_{1}$ . Both sections have the same cross-sectional area.
The ratio$\frac{I_{1}}{I_{2}}$ is
(a) $\frac{1}{\pi }$ (b) $\frac{2}{\pi }$ (c) $\frac{\pi }{3 }$ (d) $\frac{\pi }{6 }$