Question

The mixture of gases used by deep-sea divers is:
(A) Helium – oxygen
(B) Oxygen – nitrogen
(C) Hydrogen – nitrogen
(D) None of these

Answer 1

Hint: One of the components of the mixture is the gas that we need for breathing. The other is a noble gas present 0.0018% in air. Here, you can use this to get the correct answer to the given question.

Complete step by step solution:
We know that deep-sea divers are required to carry gas cylinders for breathing purposes while diving. The gas in the cylinder is a mixture of several gases. The gases are used keeping in mind the pressure difference below sea compared to that of the atmosphere.
We know that excess oxygen causes oxygen toxicity at a higher pressure than 6 metres underwater. Therefore, deep-sea divers use a mixture of gases and not just oxygen.
Let us discuss the different mixtures of gases used for various purposes.
For commercial and technical diving, a mixture of oxygen, nitrogen and helium is used to reduce side effects of nitrogen and toxicity of oxygen. This mixture is known as trimix.
For deep phase diving, we use a mixture of helium and oxygen. Under higher pressure, nitrogen narcosis is more prominent therefore this mixture called heliox is used to eliminate the danger completely.
A form of trimix named heliair is used that has 21:79 oxygen to nitrogen ratio and it is blended easily from helium and air without having to use pure oxygen.
There are other mixtures named hydreliox, hydroxy and neox used for other purposes depending upon the depth of water.
We can understand from the above discussion that deep-sea divers use a mixture of helium and oxygen.

Therefore, the correct answer is option (A) helium-oxygen.

Note: We know that air is a mixture of 21% oxygen, 78% nitrogen and 1% of other noble gases. The most common diving gas consists of a mixture of oxygen and nitrogen but due to high-pressure underwater nitrogen causes anaesthetic effect and thus it is considered safe only about 130 feet underwater.
This was also used by deep-sea divers earlier but due to side effects caused by nitrogen it is no longer considered safe and nitrogen was replaced by helium.