The correct answer is D) Low oxygen alarm. Inert gas systems are used on ships to prevent the risk of explosions in cargo tanks. These systems generate inert gas, typically from the ship's boilers, and distribute it to the cargo tanks. The key components of an inert gas system include the gas generator, scrubber, and deck seal. The alarms found on an inert gas system are low pressure alarm (A), scrubber high water level alarm (B), and deck seal low water alarm (C). However, a low oxygen alarm is not a required alarm for an inert gas system, as the purpose is to maintain an inert, oxygen-depleted atmosphere in the cargo tanks. Therefore, option D is the correct answer.