Which of the following is considered a gaseous dielectric medium?

What is the ratio of the capacitance of a capacitor with a dielectric material to its capacitance with vacuum (or air) called?

Which of the following is an example of a polar dielectric?

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 linear isotropic dielectric substance is not zero even 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: