Van De Graaff Generator

Consider the principle of Van de Graaff generator. Now choose the correct statement(s) from the following.

In a Van de Graaff type generator, a spherical metal shell is to be $15\times {10}^6 \mathrm{V}\mathrm{ }$ electrode. The dielectric strength of the gas surrounding the electrode is $5\times {10}^7 \mathrm{V}\mathrm{ }{\mathrm{m}}^{-1}$ . The minimum radius of the spherical shell required is

Which of the following statements is/are true about the principle of Van de Graaff generator?

The radius of the dome of a Van de Graaff generator is $0.13 \mathrm{m}$. If dielectric strength of the surrounding air is $3\times {\mathrm{10}}^6 \mathrm{V} {\mathrm{m}}^{-1}$ then, the maximum magnitudes for the charge and potential of the dome are given by,