Why can a metal not be used as a dielectric in a capacitor?

Can a metal be used as a medium for a dielectric?

Which of the following is the dimensional formula for electric polarisation?

The electric force acting between two point charges kept at a certain distance in vacuum is $16 \ N$. If the same two charges are kept at the same distance in a medium of dielectric constant $8$,the electric force acting between them is . . . . . . .

The unit of intensity of polarization is . . . . . . .

The unit of polarizability of the molecule is . . . . . . .