Question

The gas mixture which is used by divers inside the sea is:
(A) ${{O}_{2}}+{{N}_{2}}$
(B) ${{O}_{2}}+Ar$
(C) ${{O}_{2}}+Xe$
(D) ${{O}_{2}}+He$

Answer 1

Hint: Excess of any one of the constituents of air can be harmful for our body. Therefore mimicking the atmospheric concentration is the best precaution.

Complete answer:
The “Air” in very simple terms is defined as a homogenous mixture of gases, dust particles and water vapour. The gaseous contents include:
- Nitrogen (${{N}_{2}}$) about $78\%$
- Oxygen (${{O}_{2}}$) $21\%$
-Argon ($Ar$) nearly $0.9\%$
The above 3 gases being the most prevalent, let us not forget other ones with a lesser share but significant impact such as carbon dioxide, nitrous oxides, methane, ozone, oxides of sulphur, phosphorus etc.
Our lungs are not capable of filtering oxygen dissolved in the water molecules and therefore gas cylinders are required to supply the same. The constituents of these cylinders should be highly regulated so as to suit the needs of our body under water and also when we are slowly rising out of it. Here’s what happens:
- During deep sea dives the water pressure around us is immense and therefore we take in a lot more air than we need to. Taking in too much oxygen can cause seizures and even unconsciousness. This is referred to as oxygen toxicity which is harmful for our respiratory system.
- Breathing in excess of nitrogen is more harmful and common than oxygen. Nitrogen is not used by our bodies and stays inside our blood and tissues while we are still inside water. When we swim towards the surface due to decrease in our surrounding water pressure, this nitrogen tries to escape while taking the form of bubbles. This phenomenon is called decompression sickness or more commonly as bends can cause nerve-breaking pain in the joints.
- Nitrogen narcosis happens when under high pressure nitrogen affects our cognitive functions and makes us delusional.
To prevent all of this the diving tanks have to be filled with gases similar to the atmospheric composition along with inert gases such as Helium.
Therefore the answer to the above question is (D) ${{O}_{2}}+He$

Note:
The specific gases used in the diving tanks are specially designed so as to incorporate both the required depth and frequency of diving. Most commonly used gaseous mixtures are nitrox, heliox and hydrox.