What is a dielectric?

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

The dielectric constant $K$ of an insulator cannot be

How does the polarised dielectric modify the original external field inside it?

Explain the polarization of a polar molecule in a uniform electric field.

$Assertion \; (A)$: Non-polar materials do not have any permanent dipole moment.
$Reason \; (R)$: When a non-polar material is placed in an electric field,the centre of the positive charge distribution of its individual atom or molecule coincides with the centre of the negative charge distribution.
In the light of the above statements,choose the most appropriate answer from the options given below: