Helium is added to the oxygen supply used by deep sea divers because

Options

A. It is less soluble in blood than nitrogen at high pressure
B. It is lighter than nitrogen
C. It is readily miscible with oxygen
D. It is less poisonous than nitrogen

Answer

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks why helium is added to the oxygen supply for deep-sea divers.

2. **Historical Context**: Initially, divers used a mixture of oxygen (O2) and nitrogen (N2). However, this combination posed risks due to the effects of nitrogen on the body.

3. **Identifying the Problem with Nitrogen**: When divers ascend from deep underwater, nitrogen can form bubbles in the bloodstream, leading to a condition known as decompression sickness or "the bends." This condition is painful and can be dangerous.

4. **Introducing Helium**: To mitigate the risks associated with nitrogen, helium is introduced into the breathing gas mixture.

5. **Properties of Helium**: Helium has low solubility in blood compared to nitrogen. This means that when divers ascend, helium does not form bubbles in the bloodstream as easily as nitrogen does.

6. **Additional Benefits**: Helium is also non-flammable, which adds to its safety as a component of the breathing gas mixture.

7. **Conclusion**: The primary reason for adding helium to the oxygen supply for deep-sea divers is that it is less soluble in blood than nitrogen at high pressure, reducing the risk of decompression sickness.

### Final Answer:
Helium is added to the oxygen supply used by deep-sea divers because it is less soluble in blood than nitrogen at high pressure, which helps prevent the formation of bubbles in the bloodstream and reduces the risk of decompression sickness.

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