c
(c)
Between point $2$ and $3$
$P_0+\rho g h^{\prime}+\frac{1}{2} \rho v^2=\sigma g h^{\prime}+P_0 \quad\left[P_0=\text { atmospheric pressure }\right]$
$\Rightarrow \rho g h^{\prime}+\rho g h=\sigma g h^{\prime} \quad[\because v=\sqrt{2 g h}]$
So, $h^{\prime}=\frac{h \rho}{\sigma-\rho}$
