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

Which of the following statements is false in the case of polar molecules?

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

The function of a dielectric in a capacitor is

If the dielectric constant and dielectric strength are denoted by $k$ and $x$ respectively,then a material suitable for use as a dielectric in a capacitor must have

The dielectric constant of a metal is ........ .