A solid sphere of radius $$R$$ has a charge $$+2Q$$. A hollow spherical shell of radius $$3R$$ placed concentric with the first sphere has net charge $$-Q$$. What would be the final distribution of charges, if a conducting wire joins the spheres?
All the charge on a metallic body resides on its outer surface. Therefore upon joining the spheres with a conducting wire, the net charge = $$ 2Q-Q=Q $$ resides on the outer surface of the outer hollow shell and zero charge resides on the inner sphere.