Two spheres of radius $R$ and $2R$ having charge $Q$ and $2Q$ respectively are placed far away from each other. How much charge will flow when key $k$ is pressed?

Assertion $:-$ The maximum charge that can be given to a conductor of fixed volume depends on its shape.
Reason $:-$ If the electric field near the conductor is sufficient for dielectric breakdown of air,no more charge can be transferred to it.

$A$ point charge $q$ is placed in a cavity in a metal block. If a charge $Q$ is brought outside the metal,then the electric force experienced by $q$ is

For a spherical shell,which of the following statements is correct?

Two spherical conductors $A$ and $B$ of radii $1 \ mm$ and $2 \ mm$ are separated by a distance of $5 \ cm$ and are uniformly charged. If the spheres are connected by a conducting wire,then in the equilibrium condition,the ratio of the magnitude of the electric fields at the surfaces of spheres $A$ and $B$ is:

Two thin conducting concentric shells of radii $R$ and $2R$ are shown in the figure. The outer shell carries a charge $+Q$ and the inner shell is neutral. When the switch $K$ is closed,which of the following statement$(s)$ is/are correct?
$(a)$ The potential on the inner shell becomes zero.
$(b)$ The charge on the inner shell is $\frac{Q}{2}$.