The air that a scuba diver breathes is pressurized to counteract the pressure exerted by the surrounding water. Under these conditions, excessive amounts of nitrogen dissolves in bodily fluids, such as blood. If the diver ascends to the surface too rapidly, the excessive nitrogen bubbles out of the bodily fluids—much like carbon dioxide bubbles out of a soda immediately after it has been opened. This results in a painful and potentially lethal medical condition known as the bends. Why does breathing a mixture of helium and oxygen rather than air help divers to avoid getting the bends?
A) Oxygen and helium have stronger attractions for each other than they do for the blood, so less helium will be dissolved in the blood and to cause the bends.
B) The helium is less soluble in the bodily fluids and so less dissolves for a given pressure. Upon decompression, there is less helium to "bubble out" and cause potential harm.
C) The nitrogen in the blood will bind to helium, and so will be exhaled rather than being stuck in the blood.
D) Helium is a smaller molecule than nitrogen, so when it bubbles out of solution, it is less painful and less harmful to the body.
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