What property of a radio wave defines its polarization?

The polarization of a radio wave is defined by the orientation of its electric field. Radio waves are electromagnetic waves, which means they consist of both an electric field and a magnetic field oscillating perpendicular to each other and to the direction of wave propagation. The electric field's orientation can vary in different directions, which is what determines the polarization of the wave.

For example, if the electric field oscillates vertically, the wave is vertically polarized, whereas if it oscillates horizontally, the wave is horizontally polarized. Polarization can be linear, circular, or elliptical, depending on how the direction of the electric field changes over time.

The other aspects of radio wave properties mentioned in the choices pertain to the wave's structure but do not define its polarization. The magnetic field's orientation contributes to the overall wave but isn't the factor that defines polarization. The ratio of energy in the two fields or the velocity to wavelength does not relate to polarization characteristics. Thus, understanding that polarization is fundamentally linked to the electric field's orientation is critical.