The charge given to any conductor resides on its outer surface,because

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

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

$A$ spherical conducting shell of inner radius $r_1$ and outer radius $r_2$ has a charge $Q$.
$(a)$ $A$ charge $q$ is placed at the centre of the shell. What is the surface charge density on the inner and outer surfaces of the shell?
$(b)$ Is the electric field inside a cavity (with no charge) zero,even if the shell is not spherical,but has any irregular shape? Explain.

Which of the following statements is $NOT$ true for a charged conducting sphere?

Two insulated charged spheres of radii $20\,cm$ and $25\,cm$ respectively and having an equal charge $Q$ are connected by a copper wire,then they are separated.