What is a linear isotropic dielectric?

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

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: Net dipole moment of a polar dielectric substance is zero in the absence of an external electric field.
Reason $(R)$: In the absence of an external electric field,the different permanent dipoles of a polar dielectric substance are oriented in random directions.
In the light of the above statements,choose the most appropriate answer from the options given below.

Write the types of dielectrics and explain them. Give some examples of dielectric substances.

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

Write the relation between $\vec{P}$ and $\vec{E}$ for a linear isotropic dielectric.