To solve this problem, we need to understand the nature of polar molecules.$\\$• Polar molecules are characterized by having a permanent electric dipole moment.$\\$• This means that the centers of positive and negative charges in the molecule do not coincide,$\\$ resulting in a net dipole moment.$\\$Let's analyze the given options:$\\$Option 1: $$having zero dipole moment.$\\$• Molecules with zero dipole moment are non-polar, not polar.$\\$Option 2: $$acquire a dipole moment only in the presence of an electric field due to displacement of charges.$\\$• This describes induced dipole moments, which occur in non-polar molecules under an external electric field.$\\$Option 3: $$acquire a dipole moment only when magnetic field is absent.$\\$• Magnetic fields do not directly affect the electric dipole moment of molecules.$\\$Option 4: $$having a permanent electric dipole moment.$\\$• This is the correct definition of polar molecules. They have a permanent dipole moment due to$\\$ the uneven distribution of charges within the molecule.$\\$Therefore, the correct option is Option 4: having a permanent electric dipole moment.