Question

Percentage of oxygen in atmosphere of earth is:
A. $42.94\% $
B. $20.94\% $
C. $35.94\% $
D. $25.94\% $

Answer 1

Hint: We need to know about the earth’s atmosphere and its composition. The atmosphere is made up of a mixture of gases such nitrogen, oxygen, and carbon-dioxide. There is no exact boundary between the atmosphere and outer space but becomes thinner as we go higher. The purity of air present in the atmosphere is defined by its oxygen content. Oxygen is the most important component of the atmospheric gases as we need oxygen to breathe and for the minimum survival of all living beings.

Complete step by step answer:
We must need to remember that the Earth is the only planet in the galaxy which has an atmosphere which can sustain life. The gases of the atmosphere not only contain the air that we breathe but also gases that protects us from the heat and radiation coming from the sun. The gases play an important role in the cooling and warming of the earth’s surface. The composition is given below:
Nitrogen — $78\% $
Oxygen — $21\% $
Carbon dioxide — $0.04\% $
Trace amounts of other gases such as argon, helium, methane, hydrogen etc.
The given data speaks only the approximate values of composition in percentage for pure dry air.

So, the correct answer is Option B.

Note: We must be noted the composition of air is not fixed through the entire atmosphere. It depends from places to places depending on pollution. In industrial areas where there is emissions of smoke in the atmosphere, oxygen levels decrease and the composition of other harmful gases in the atmosphere increases. This is basically what is called air pollution. Other planets such as Venus contain a fully carbon dioxide composed atmosphere with traces of nitrogen and sulphuric acid hence survival is not possible on the planet.