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 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 :

• A

  (A) is correct but $(\mathrm{R})$ is not correct
• B

  Both $(\mathrm{A})$ and $(\mathrm{R})$ are correct but $(\mathrm{R})$ is not the correct explanation of (A)
• C

  Both (A) and (R) are correct and (R) is the correct explanation of (A)
• Correct answer
  D

  (A) is not correct but $(\mathrm{R})$ is correct

Hence, the correct answer is option: 'D'.