Polarization in a dielectric on application of an electric field refers to the displacement or separation of opposite charge centers within the dielectric material. This phenomenon occurs due to the alignment of the electric dipoles present in the dielectric material in response to the applied electric field.

The electric dipoles in a dielectric material consist of positive and negative charges that are separated by a small distance. In the absence of an external electric field, these dipoles are randomly oriented, resulting in a net zero polarization. However, when an electric field is applied, the dipoles tend to align themselves along the direction of the field.

The polarization of a dielectric material can be explained through the following points:

1. Displacement/separation of opposite charge centers: The applied electric field exerts a force on the charges within the dielectric material, causing them to separate or displace from their original positions. The positive charges are attracted towards the negative terminal of the applied field, while the negative charges are attracted towards the positive terminal. This separation of charges creates an electric dipole moment within the dielectric, resulting in polarization.

2. No passing of current through the dielectric: Unlike conductors, dielectric materials do not allow the flow of electric current. The polarization of a dielectric does not involve the movement of charges, but rather the alignment of existing charges. Therefore, the passing of current through the dielectric is not a characteristic of polarization.

3. Excitation of electrons to higher energy levels: The process of polarization does not involve the excitation of electrons to higher energy levels. Instead, it involves the alignment of existing dipoles within the dielectric material. The energy levels of the electrons remain unchanged during polarization.

In conclusion, the correct answer is option 'A' - polarization in a dielectric on the application of an electric field results in the displacement or separation of opposite charge centers within the dielectric material.