What happens to the polarization of an electromagnetic wave when it leaves a vertically polarized antenna?

When an electromagnetic wave is radiated from a vertically polarized antenna, it maintains its vertical polarization as it propagates through free space. This is due to the nature of how the electromagnetic wave is produced; the oscillating electric field associated with this wave aligns vertically in relation to the ground as determined by the orientation of the antenna.

Practically, this means that if you were to measure the electric field component of the radiated wave, you would consistently find it aligned vertically, as long as other environmental factors (like reflections or interactions with materials) do not alter its state.

Options suggesting that the wave becomes horizontally polarized, unpolarized, or loses all polarization are not consistent with how wave polarization works and how antennas emit waves. The fundamental nature of the polarization remains aligned with the orientation of the transmitting antenna until acted upon by external factors.