In deep-sea diving, divers use a mixture of gases consisting of oxygen and A. Hydrogen B. Nitrogen C. Argon D. Helium

The correct answer is D. Helium.

When divers go deep underwater, the pressure of the water increases. This increased pressure can cause nitrogen to dissolve in the blood and tissues. If the diver ascends too quickly, the nitrogen can come out of solution and form bubbles in the blood and tissues, a condition known as decompression sickness, or “the bends.”

Helium is less soluble in blood and tissues than nitrogen, so it is less likely to cause decompression sickness. Additionally, helium is lighter than nitrogen, so it helps to reduce the risk of nitrogen narcosis, a condition that can occur when divers breathe air at high pressures.

For these reasons, helium is the gas of choice for deep-sea diving.

Here is a brief explanation of each option:

• Hydrogen is a flammable gas, so it is not safe to use in diving.
• Nitrogen is the most common gas in air, but it can cause decompression sickness.
• Argon is a noble gas that is not very reactive. It is not used in diving because it is not as effective as helium
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  at reducing the risk of decompression sickness.
• Helium is a noble gas that is less soluble in blood and tissues than nitrogen. It is also lighter than nitrogen, so it helps to reduce the risk of nitrogen narcosis.