Which inert gas is mixed with oxygen gas by deep-sea divers to adjust the partial pressure of oxygen gas?

Explanation

The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen below those of air, to allow the gas mix to be breathed safely on deep dives. A mix of helium and oxygen is often used by deep sea divers for breathing because it reduces the risk of developing decompression sickness, also known as "the bends." The bends can occur when a diver ascends too quickly from a deep dive, causing nitrogen bubbles to form in their bloodstream and tissues. These bubbles can cause joint pain, fatigue, and even neurological damage in severe cases. Helium, which has a lower molecular weight than nitrogen, is less soluble in blood and tissues and therefore reduces the risk of bubble formation during ascent. Oxygen, on the other hand, is essential for sustaining life and provides the necessary gas for cellular respiration. However, high levels of oxygen can be toxic to the body and can cause seizures and other adverse effects. Therefore, a mixture of helium and oxygen is used to balance the benefits of reduced nitrogen exposure with the need for a sufficient oxygen supply.