What property of a radio wave defines its polarization?

A radio wave is an electromagnetic wave, meaning it is made up of both an electric field and a magnetic field traveling together at right angles to each other. By scientific convention, the polarization of a radio wave is strictly defined by the orientation of its electric field. If an antenna's radiating elements are vertical to the ground, the emitted electric field is vertical, resulting in a vertically polarized wave. It is incorrect to use the magnetic field to define polarization, even though both fields are present in the wave. Options suggesting ratios of energy or velocity describe entirely different wave characteristics and have nothing to do with polarization.