Environmental Chemistry - Composition of air: Important 25 MCQs

Welcome to the COMPETITIVE EXAM MCQs SERIES of ENVIRONMENTAL SCIENCE for UGC-NET/JRF, SLET, GATE, and other entrance tests: Environmental Chemistry – Composition of Air.

Syllabus outline

Components and structure of Earth’s atmosphere.
The role of air in environmental systems and its importance in environmental chemistry.
Trace gases, including greenhouse gases and their impact on global climate change.
Assessment of pollutant gases (e.g. effects on air quality and human health).
Study of suspended particulate matter and its sources.
Environmental and health implications of particulate matter in the atmosphere.
Regulatory framework for controlling air pollution.
Knowledge of air quality standards and monitoring methods.
Identification and study of major gases present in the atmosphere.
A discussion of global environmental challenges related to air composition and pollution is also included.

Quick Study Guide

The chemical composition of the Earth’s atmosphere provides the baseline matrix for meteorological dynamics, global biogeochemical cycles, and photochemical pollution models. Understanding this domain requires analysing atmospheric stoichiometry, thermodynamic stratification, and the specific kinetic behaviours of trace gases and aerosols.

Atmospheric Stoichiometry and Origins: Earth’s modern secondary atmosphere evolved via geologic outgassing and biological photosynthesis. The distribution of permanent gases varies between volumetric and gravimetric measurements (e.g., N₂ constitutes ~78% by volume but ~75.5% by weight). Trace gases possess specific biogeochemical origins, such as Argon-40 deriving primarily from the radiogenic decay of crustal Potassium-40.
Vertical Thermal Stratification: The atmosphere is structurally stratified by altitudinal temperature gradients (lapse rates). The troposphere and mesosphere exhibit a positive lapse rate (temperature decreases with elevation). In contrast, the stratosphere and thermosphere exhibit pronounced temperature inversions, driven respectively by ozone absorbing ultraviolet radiation and atomic oxygen absorbing extreme ultraviolet radiation.
Tropospheric Kinetics and Aerosols: The troposphere functions as a dynamic chemical reactor for primary emissions. The aerodynamic diameter of particulate matter strictly dictates its atmospheric residence time, gravitational settling velocity, and optical properties (scattering and absorption), which govern both urban visibility degradation and the long-range aeolian transport of bioaerosols.
Respiratory Gas Exchange Dynamics: Biological respiration fundamentally alters local atmospheric stoichiometry. While inert gases like nitrogen remain metabolically unutilized (maintaining equal inhaled and exhaled partial pressures), alveolar gas exchange significantly depletes O₂ concentrations while exponentially increasing CO₂ and H₂O vapour, shifting the thermodynamic properties of the exhaled air mass.
Ionospheric Physics: The upper thermosphere transitions into the ionosphere, a continuous zone of free electrons and ionised molecular plasma generated by high-energy solar extreme ultraviolet and X-ray radiation. This plasma dictates upper-atmospheric electrodynamics, geomagnetic field interactions, the refraction of high-frequency radio waves, and the precipitation of charged solar wind particles that trigger auroral emissions.

Test Your Knowledge

This quiz contains 25 concept-based MCQs on the Composition of Air. Each question has a single correct/most appropriate answer.

1. What is the origin of the Earth’s atmosphere?

a) Anthropogenic activity

b) Volcanic activity

c) Biological activity

d) Both Volcanic and Biological activity

2. What is the primary function of argon (Ar) in the atmosphere?

a) It provides oxygen for breathing.

b) It supports combustion.

c) It serves as a noble gas with no significant reactivity.

d) It is a greenhouse gas.

3. Which of the following is NOT a common method for measuring air quality?

a) Barometric pressure measurements

b) Gravimetric analysis

c) Remote sensing via satellites

d) Gas chromatography

4. What is the fastest recorded gust of wind on Earth?

a) 322 Km/h

b) 161 Km/h

c) 408 Km/h

d) 5 Km/h

5. In which atmospheric layer do weather phenomena such as clouds and precipitation occur?

a) Mesosphere

b) Thermosphere

c) Troposphere

d) Stratosphere

6. What are bioaerosols?

a) Insects that can fly long distances

b) Microscopic organisms that travel through the air

c) Microorganisms that live in soil and water

d) Birds that migrate using wind currents

7. In human-exhaled air, which gas concentration is the highest?

a) Water vapour

b) Carbon dioxide

c) Oxygen

d) Nitrogen

8. What is the third most abundant gas in Earth’s atmosphere?

a) Oxygen

b) Nitrogen

c) Argon

d) Carbon dioxide

9. Which is NOT a regulatory measure to control air pollution?

a) Carbon offset programs

b) Emission standards for vehicles

c) Ambient air quality standards

d) Industrial emissions permits

10. Which layers of Earth’s Atmosphere are marked by a decrease in temperature with an increase in elevation?

a) Troposphere and Stratosphere

b) Mesosphere and Thermosphere

c) Stratosphere and Mesosphere

d) Troposphere and Mesosphere

11. What gas is used in airbags to inflate them rapidly during a car collision?

a) Nitrogen

b) Carbon dioxide

c) Oxygen

d) Helium

12. What are the criteria pollutants?

a) Gases that are harmless to humans

b) Gases responsible for climate change

c) Pollutants that have set air quality standards

d) Gases that are naturally occurring

13. Which of the following is the correct average gas proportions by weight in the atmosphere?

I – 75.47% Nitrogen

II – 23.2% Oxygen

III – 1.28% Argon

IV – 0.062% Carbon Dioxide

a) I and II

b) I, II, III and IV

c) Only I

d) I, II and III

14. How do bioaerosols primarily move through the air?

a) By flying like birds

b) Via wind, rain, or sneezing

c) Through the use of tiny wings

d) By attaching to larger airborne particles

15. What is the significance of international agreements and protocols related to air quality and climate change?

a) They focus solely on regional air quality issues.

b) They establish legally binding targets and guidelines.

c) They provide funding for air quality research.

d) They have no impact on global air quality.

16. Helium (He) is known for its low density and is used in which of the following applications?

a) Scuba diving tanks

b) Balloon Inflation

c) Breathing masks for medical patients

d) Rocket propulsion

17. What is the approximate percentage of nitrogen in the Earth’s atmosphere by weight?

a) 95

b) 47

c) 2

d) 08

#18. What is the approximate percentage of oxygen in exhaled air?

a) 4%

b) 04%

c) 21%

d) 4%

19. What is the main source of argon in the atmosphere?

a) Bacterial activities

b) Volcanic eruptions

c) Burning of fossil fuels

d) Radioactive decay in rocks

20. What is one of the main factors contributing to the wind’s ability to transport particles over long distances?

a) Particle size

b) Wind-resistant particles

c) The time of day

d) The temperature of the air

21. Air quality indices (AQI) are used to:

a) Measure ozone depletion.

b) Measure greenhouse gas concentrations.

c) Assess and communicate air quality to the public.

d) Monitor changes in atmospheric pressure.

22. Which of the following is mainly responsible for the hazy appearance of smog in urban areas?

a) Carbon dioxide

b) Nitrogen

c) Particulate matter

d) Oxygen

23. Which of the following correlations between inhaled (I) and exhaled (E) air is correct?

I – Nitrogen (I > E)

II – Oxygen (I > E)

III – Carbon dioxide (I < E)

IV – Water vapour (I < E)

a) II, III and IV

b) I, II and IV

c) Only III

d) II and III

24. Water vapour in the atmosphere is crucial for which of the following?

a) Generating ozone in the stratosphere

b) Regulating air pressure

c) Weather patterns and climate regulation

d) Shielding the Earth from solar radiation

25. What is the ionosphere?

a) The layer of the atmosphere where the ozone layer is located.

b) The layer of the atmosphere where satellites orbit.

c) The layer of the atmosphere closest to the Earth’s surface.

d) The layer of the atmosphere where auroras occur.

Previous: Fundamentals of Environmental Chemistry

Next: Chemical speciation

References

Frederick K. Lutgens, Edward J. Tarbuck, Redina L. Herman (2019). The Atmosphere: An Introduction to Meteorology, Pearson, 14^th edition.
John H. Seinfeld, Spyros N. Pandis (2016). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, John Wiley & Sons, 3rd edition.
C. Donald Ahrens and Rober Henson (2022). Meteorology Today: An Introduction to Weather, Climate, and the Environment, Cengage Learning, 13^th edition.
De, Anil Kumar and De, Arnab Kumar (2024). Environmental Chemistry, New Age International, 11^th Edition.