$A$ charged spherical conductor of radius $R$ is connected momentarily to another uncharged spherical conductor of radius $r$ by means of a thin conducting wire. Then,the ratio of the surface charge density of the first to the second conductor is:

Given below are two statements.
Statement $I$ : Electric potential is constant within and at the surface of each conductor.
Statement $II$ : Electric field just outside a charged conductor is perpendicular to the surface of the conductor at every point.
In the light of the above statements,choose the most appropriate answer from the options given below.

$A$ charge $q$ is placed at $O$ in the cavity of a spherical uncharged conductor. Point $S$ is outside the conductor. If the charge is displaced from $O$ towards $S$ while still remaining within the cavity,then:

$A$ point charge is kept at the centre of a metallic insulated spherical shell. Then:

Two concentric spherical shells of radius $R_1$ and $R_2$ have $q_1$ and $q_2$ charge respectively as shown in the figure. How much charge will flow through key $k$ when it is closed?

'Inside a conductor,the electrostatic field is zero'. Explain.