Important Gases & Composition of Air

5 min

Master key properties, percentages, and exam-favourite facts about atmospheric gases.

Golden Rule of Air Composition

Dry air is dominated by nitrogen at 78% and oxygen at 21%, while noble gases and carbon dioxide make up the remaining 1%. Always remember these volume percentages for direct exam questions.

Exam Value & Weightage

Direct questions on air percentage composition appear in SSC and Railway exams.
Greenhouse gases and ozone depletion questions are core to Defence and CAPF GS.
Properties of hydrogen and carbon dioxide form the basis of chemical science MCQs.

Smart Memory Hooks

N2 is No-burn (dilutes oxygen fire), O2 is Life-support, CO2 is Soda-fizz.
Ozone has 3 oxygen atoms (O3) acting as an umbrella in the stratosphere.
Hydrogen is lightest (H2), floats away, and is known as future fuel.

Atmospheric Gas Composition Table

Gas Name	Formula	Percentage (%)
Nitrogen	N2	78.08%
Oxygen	O2	20.95%
Argon	Ar	0.93%
Carbon Dioxide	CO2	0.04%

Key Gas Profiles

Ozone (O3)

(UV Shield layer)

UV Shield layer

Absorbs harmful ultraviolet rays in the stratosphere.

Hydrogen

(Lightest element)

Lightest element

Highly flammable gas known as the fuel of the future.

CO2

(Greenhouse gas)

Greenhouse gas

Traps planetary heat and causes global warming.

Nitrogen

(Inert buffer gas)

Inert buffer gas

Prevents rapid combustion and preserves packaged foods.

Common Exam Traps

Carbon dioxide is the 3rd most abundant gasArgon is 3rd, CO2 is 4th

Argon (0.93%) is greater in volume than carbon dioxide (0.04%).

Ozone layer is in the troposphereOzone layer is in the stratosphere

Most atmospheric ozone resides in the stratosphere layer (15-50 km).

Nitrogen supports combustion directlyNitrogen dilutes combustion speed

Nitrogen is inert and prevents objects from burning too fast.

Quick Exam Test

Q1.Which gas is present in the maximum percentage in Earth's atmosphere?

Q2.In which atmospheric layer is the ozone layer primarily found?

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