Question: 20. Polar molecules are the molecules:
(1) having zero dipole moment.
(2) acquire a dipole moment only in the presence of electric field due to displacement of charges.
(3) acquire a dipole moment only when magnetic field is absent.
(4) having a permanent electric dipole moment.
Answer: Option (4)
Explanation:
A polar molecule is one in which the centres of positive and negative charges do not coincide.
Due to this separation of charges, the molecule possesses a non-zero dipole moment even in the absence of any external electric field.
Such molecules are said to have a permanent electric dipole moment.
Non-polar molecules either have symmetric charge distribution or
acquire a dipole moment only when an external electric field is applied.
Therefore, polar molecules are those having a permanent electric dipole moment,
and the correct answer is Option (4).