Which gas in larger quantities enhances the Nitrox mixture for divers?

The enhancement of a Nitrox mixture for divers primarily comes from the addition of oxygen. In the context of nitrox diving, this refers to the combination of oxygen with nitrogen to create a gas mixture that has a higher percentage of oxygen than normal air, which is about 21% oxygen and 79% nitrogen.

Increasing the oxygen content in the mixture helps to reduce the risk of nitrogen narcosis and decompression sickness by allowing divers to use less nitrogen, which is the gas that can lead to these issues at greater depths and longer exposures. The higher levels of oxygen can also provide some physiological benefits, such as improved oxygen delivery to tissues, which is why many divers choose to use Nitrox mixtures during their dives.

Helium, while useful in reducing narcosis at great depths and often mixed in with nitrox for technical divers (particularly in trimix), does not enhance the Nitrox mixture in the same way as oxygen does. Similarly, argon is largely used for dry suit insulation rather than enhancing a breathing gas mix. Nitrogen, being the primary component of air, does not enhance a Nitrox mixture when aiming for the benefits that a higher oxygen content provides. Thus, oxygen is the gas in larger quantities that enhances Nitrox mixtures