Height of capillary rise in tube is given by $h=\frac{2T\cos \theta }{r\rho g}$, here, $T$is surface tension, $\theta$ is angle of contact, $r$ is radius of capillary tube and $\rho$ is density of liquid.

Here, $h_1=\frac{2T}{r_1\rho g}$ and $h_2=\frac{2T}{r_2\rho g}$

Now, the difference in liquid evels in the two limbs is

 $$\begin{gathered} h=h_1-h_2 \\ =\frac{2T}{\rho g}\left(\frac{1}{r_1}-\frac{1}{r_2}\right) \\ =\frac{2\times 0.03}{1500\times 10}\left(\frac{1}{2\times {10}^{-3}}-\frac{1}{4\times {10}^{-3}}\right) \\ =0.001 \mathrm{m}=1 \mathrm{mm} \end{gathered}$$