Solve this:

Q. A cylindrical capacitor has two co-axial cylinders of length 20 cm and radii 2r and r. Inner cylinder is given a charge 10 $\mathrm{\mu }$C and outer cylinder a charge of -10 $\mathrm{\mu }$C. The potential difference between the two cylinders will be 

$$\begin{gathered} \left(1\right) \frac{0.1 \mathrm{In} 2}{4{\mathrm{\pi \epsilon }}_0} \mathrm{mV} \left(2\right) \frac{\mathrm{In} 2}{4{\mathrm{\pi \epsilon }}_0} \mathrm{mV} \\ \left(3\right) \frac{10 \mathrm{In} 2}{4{\mathrm{\pi \epsilon }}_0} \mathrm{mV} \left(4\right) \frac{0.01 \mathrm{In} 2}{4{\mathrm{\pi \epsilon }}_0} \mathrm{mV} \end{gathered}$$