To avoid cavitation in the pump, the pressure at the highest point of the system should be at least equivalent to a head of water of:

To prevent cavitation in a pump, it is essential to maintain adequate pressure at the pump's inlet, particularly at the highest point in the system. Cavitation occurs when the pressure drops below the vapor pressure of the liquid, causing vapor bubbles to form, which can lead to pump damage when they collapse.

The correct choice reflects an understanding of the atmospheric pressure's role at sea level, which is about 101.3 kPa or equivalent to a column of water. A head equivalent to 1.2 meters (4 feet) is significant because it assures that there's sufficient pressure to keep the liquid from reaching its vapor pressure at the pump inlet, thus preventing cavitation under most operating conditions.

In many systems, a minimum pressure of 1.2 meters is adequate under typical conditions, allowing for some safety margin for head loss due to friction in the piping and other losses that might occur.

Other choices may suggest a lower head which could be insufficient to counterbalance the potential losses and ensure stable operation of the pump. Consequently, maintaining at least a 1.2 meter head provides a practical level of safety against cavitation.