ICAO Doc 8984 - Manual of Civil Aviation Medicine
Underwater diving

26. If you go flying after scuba diving or any underwater activity using compressed air, you should be aware that if insufficient time has elapsed between surfacing and take-off, the medical consequences can be serious or even fatal. Due to greatly increased pressures underwater, nitrogen is absorbed into the blood and tissues. The amount depends on the depth and duration of exposure. If take-off follows the dive too soon to allow the body to rid itself normally of this excess nitrogen, the gas may form bubbles in the blood or tissues causing discomfort, pain, difficulty in breathing, or even death, at altitudes of 7000 ft (2135 m) or less, altitudes attained by most light aircraft. Older or overweight individuals are more susceptible to this condition. As a general rule, individuals should not fly within 12-48 hours following diving using compressed air, the difference depending mainly on the duration and how deep the dive(s) were.

Let's examine the given options:

The pilot may not fly for 24 hrs. → CORRECT. Individuals should not fly within 12-48 hours following scuba diving. The limit of 24 hours falls within that range.

The pilot may fly immediately if they did not exceed 10 meters depth. → INCORRECT. Even shallow dives can leave dissolved nitrogen in the blood. The pilot may not fly immediately to allow time for the nitrogen bubbles to dissolve into the blood.

The pilot should wait 48 hours only if they used nitrox. → INCORRECT. Nitrox (a type of breathing gas used in scuba diving that contains more oxygen and less nitrogen than normal air) does not create a special 48-hour rule. The timing depends mainly on the duration and how deep the dive(s) were.

The pilot may fly after 12 hours regardless of the dive profile. → INCORRECT. Individuals should not fly within 12-48 hours following diving, and the timing depends on the duration and how deep the dive(s) were.