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Composition of Air

Composition of Air – Oxygen, Carbin Dioxide, Nitrogen, Argon, Water Vapour, Dust Particles, Practice Problems and FAQ

We are well aware that although global warming has been continuing for a very long time, it has accelerated significantly during the past century due to the burning of fossil fuels, which creates a "greenhouse effect" in the Earth's atmosphere.

Because of the greenhouse gases produced when fossil fuels are burned, heat cannot escape from the atmosphere. Carbon dioxide is the main greenhouse gas. Only 0.03 percent of the air in our atmosphere is carbon dioxide. The atmosphere also contains other greenhouse gases like nitrous oxide, water vapour, methane and fluorinated gases.

Have you ever wondered what the air that surrounds us is composed of?

Air consists of 78% nitrogen, 21% oxygen and 1% other gases. Let’s get to know about the composition of air on this concept page!


  • Composition of Air
  • Oxygen
  • Carbon Dioxide
  • Nitrogen
  • Argon
  • Water vapour
  • Dust particles
  • Practice Problems
  • Frequently Asked Questions – FAQ

Composition of Air

The most vital component of our existence is air. It is a mixture of different gases and is commonly referred to as the atmosphere. Oxygen is the first thing that springs to mind when speaking of air. Numerous other airborne substances, in addition to oxygen, are crucial for maintaining life on Earth.

20.95 percent oxygen, 78.09 percent nitrogen, 0.93 percent argon, 0.03 percent carbon dioxide, and other gases make up air. Many dust particles also include water vapour. Dry air has a molar mass of 28.79 g/mol.

As you move through the layers of the atmosphere, the composition of the air remains unchanged. The amount of molecules is what changes. Air molecules shrink and get smaller. From one location to another, the moisture content fluctuates. Comparatively speaking to wetlands, dry areas have lower moisture content.


It has the atomic number 8 and the symbol O to denote it. In the atmosphere, it is the second most prevalent element. Oxygen gas is very reactive. With other elements, it forms an oxide bond. Oxygen is quite flammable. The oxygen cycle is responsible for the exceptionally high oxygen gas content on Earth. This biogeochemical cycle (oxygen transfer between biotic and abiotic components) explains how oxygen moves between and among the atmosphere, biosphere, and lithosphere, the planet's three main oxygen reservoirs. Photosynthesis, which created the atmosphere of the modern Earth, is the major driving factor behind the oxygen cycle.

Characteristics of Oxygen

  1. It is responsible for cellular respiration. There is no human life without oxygen.
  2. It is utilised in industries to make steel by smelting iron ore. In this process, 55% of the oxygen is used.

Carbon Dioxide

There is also carbon dioxide in the atmosphere. It makes up 0.03% of the entire amount. There are trace levels of the gases in the air. Carbon has an atomic number of 6. When organic matter decomposes or breathes, CO2 is created. Additionally, geysers and hot springs are responsible for the creation of CO2.

Characteristics of Carbon Dioxide

  1. The combustion of natural gas and petroleum produces carbon dioxide.
  2. It is used in the food business to make soft drinks and candies.
  3. It is utilised in fire extinguishers
  4. It is a crucial component in the production of urea and fertilisers.
  5. It is used as a refrigerant and for food storage
  6. It produces the greenhouse effect (or) it is a greenhouse gas.
  7. It increases the atmospheric temperature, which results in global warming.


In the atmosphere, nitrogen is the most abundant. It makes up close to 78% of the air in the atmosphere. It has the atomic number 7, and its symbol is N. It is created by the nitrogen fixation process. Additionally, fractional air distillation is used in industries to create it. Two molecules of nitrogen atoms connected by a triple bond make up dinitrogen. This bond makes it tough for the substance to break down.

Characteristics of Nitrogen

  1. Nucleic acid and amino acids, both of which are present in living things, contain nitrogen.
  2. It is an important fertiliser ingredient.
  3. It has applications in pharmaceuticals, antibiotics, and medicine
  4. Due to its non-toxic qualities, it causes asphyxia. (Asphyxiation is caused by a lack of oxygen, the inability to breathe, which leads someone to die or become unconscious).


Another crucial component of air is argon. It has the atomic number 18 and the symbol Ar. Argon is created in the atmosphere when cosmic rays interact with potassium - 40. It is made for industrial use by fractional distilling liquid air.

Characteristics of Argon

  1. It is used in graphite furnaces.
  2. It is used in fluorescent lighting to prevent the oxidation of the filaments.
  3. It has no flavour, colour, or odour.
  4. It is used for medical purposes.
  5. It is used to treat eye problems as a blue laser.
  6. It is used to eliminate tumours.

Water vapour

It is present in concentrations ranging from 0.01 to 4.24 per cent.

Characteristics of Water Vapour

  1. It is a greenhouse gas.
  2. Because of its lower density than air, it is used as a lifting gas.
  3. It is used as steam for cooking and energy production.
  4. It is used to preserve the shape of a hot air balloon in the form of steam.

Dust particles

Dust particles are small, solid particulates that are present in the atmosphere. They are also referred to as Aeolians. The particles are made up of soil, pollutants, or particles from volcanic eruptions. Pollen, as well as some amounts of human and animal hair, are included in the dust particles. Due to the passage of vehicles, numerous dust particles that have been spread across the road become airborne. These dust particles cause a variety of significant issues, including respiratory ailments and allergic reactions.

The gases listed above are the primary constituents of air. Other elements found in the air include helium, neon, and sulphur. The concentration of these gases varies depending on a number of variables, including temperature, pressure, altitude, and more.

Molar Mass of dry air

Molar mass can be related to the number of moles as

Moles of dry air = Weight of dry airMolar Mass of dry air

nair=WairMMair (Here, air represents dry air).........................(1)

Wair represents the weight of all the gases present in the air. So, it can be written as


(W1,W2,W3..,Wn are the weight of gases present in air)

Substituting it in equation (1)





(MM1,MM2,MM3..,MMn are the molar masses of gases present in air)


nair=n1+n2+n3..+nn(Here  n1,n2,n3..,nn are the moles of gases present in air)

n1n1+n2+n3..+nn=x1= mole fraction


Here, xnMMn represents the contribution of the molar mass of any gas component in molar mass of dry air.

Practice Problems

Q1. Which of the following gas has a minimum contribution to the molar mass of Air?

A. Oxygen
B. Argon
C. Carbon dioxide
D. Nitrogen

Answer: C

Solution: 78% of the air is nitrogen, 21% is oxygen, 0.9% is argon, 0.03% is carbon dioxide, and 0.17 % is made up of various gases and water vapour. As you move through the layers of the atmosphere, the makeup of the air remains unchanged. Thus, it is obvious that carbon dioxide is the gas present in the atmosphere with the lowest concentration.

So, option C is the correct answer.

Q2. What will be the contribution of the molar mass of 78% nitrogen present in dry air?

A. 28.06 g
B. 21.84 g
C. 30.12 g
D. 28.97 g

Answer: B

Solution: Consider the number of molecules in dry air to be 100.

Moles of air = Given numberAvagadro Number = 100NA

Molecules of Nitrogen in dry air = 78

Moles of Nitrogen = Given numberAvagadro Number = 78NA

Mole fraction of Nitrogen =  Moles of NitrogenMoles of air  = 78NA100NA =0.78

Contribution of the molar mass of 78% Nitrogen = x×MM=0.78×28=21.84 g

So, option B is the correct answer.

Q3. What will be the molar mass of dry air when 78% nitrogen, 20% oxygen and 0.03% carbon dioxide are assumed to be present?

A. 32 g
B. 64 g
C. 28 g
D. 24 g

Answer: C

Solution: Consider the number of molecules in dry to be 100.

Moles of air = Given numberAvagadro Number = 100NA

Molecules of Nitrogen in dry air = 78

Moles of Nitrogen = Given numberAvagadro Number = 78NA

Mole fraction of Nitrogen =  Moles of NitrogenMoles of air  = 78NA100NA =0.78

Molecules of Oxygen in dry air = 20

Moles of Oxygen = Given numberAvagadro Number = 20NA

Mole fraction of Oxygen =  Moles of OxygenMoles of air = 20NA100NA =0.2

Molecules of Carbon dioxide in dry air = 0.03

Moles of Carbon dioxide = Given numberAvagadro Number = 0.03NA

Mole fraction of Carbon dioxide =  Moles of Carbon dioxideMoles of air  = 0.03NA100NA =3×10-4



MMair=21.84+6.4+0.0132=28.25 g

So, option C is the correct answer.

Q4. Which of the following statements is incorrect?

A. The atmosphere consists of 78% nitrogen
B. 21% oxygen is present in the atmosphere
C. 0.9% of the atmosphere consists of argon
D. 0.1% carbon dioxide is present in the atmosphere

Answer: D

Solution: Air consists of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide and 0.17% of other gases. Among the given statements, the statement given in option D is incorrect as the atmosphere consists of only 0.03% carbon dioxide and not 0.1%.

So, option D is the correct answer.

Frequently Asked Questions – FAQ

Q1. What exactly is the atmosphere?
The atmosphere is a protective covering of gases that protects all life on Earth by balancing temperatures within a narrow range and blocking out damaging rays of sunlight. The atmosphere consists of different layers like the troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Q2. What makes the air move?
Answer: The difference in air pressure is responsible for the movement of air. The difference in the pressure is brought out by the difference in temperatures of the air pockets as a result of uneven heating of the Earth

Q3. What creates low air pressure?
Answer: When air is heated, it becomes warm and rises, This creates low air pressure, When air is cooled, it descends and creates high pressure.

Q4. What is wind?
Answer: Air in motion is referred to as "wind." A variety of air pressures acting on the earth's surface cause the air to move. There is a lot of variation in wind speed and direction. The wind force is referred to as "cardinal points."

Related topics


Waste and Waste Management

Air Pollution

Ozone Layer depletion

Solid Pollution

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