Final answer:
An omnidirectional antenna is the best choice for ensuring maximum wireless coverage in an open green space, as it provides 360-degree coverage.
Step-by-step explanation:
To ensure maximum wireless coverage in the green space near the center of the college campus, where the antenna is being installed on a pole in the middle of the field, the ideal type of antenna to be installed is an omnidirectional antenna. Omnidirectional antennas radiate and receive signals in all horizontal directions equally, making them perfect for providing 360-degree coverage in an open area. This contrasts with bi-directional, yagi, and unidirectional antennas, which are designed to concentrate signal strength in specific directions and would not be as effective in covering a central open area.