What is the most common air or gas mixture used in recreational scuba diving.

Context: For some diving, gas mixtures other than normal atmospheric air can be used, so long as the diver is competent in their use. The most commonly used mixture is nitrox, also referred to as Enriched Air Nitrox, which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the risk of decompression sickness or allowing longer exposure to the same pressure for equal risk. The reduced nitrogen may also allow for no stops or shorter decompression stop times or a shorter surface interval between dives. A common misconception is that nitrox can reduce narcosis, but research has shown that oxygen is also narcotic.: 304

Answer: For most recreational diving atmospheric air with 21% oxygen and 78% nitrogen is used. The second most common mixture is Enriched Air Nitrox which contains extra oxygen with 32% or 36% and less Nitrogen than is found in atmospheric air, which permits divers to have shorter safety stops or shorter surface intervals.