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Tamil Nadu (TNBSE)Class 4 Science★ 4-5 marks in TN Class 4 Term 3 exams — composition of air, properties, air pollution causes and effects

Air We Breathe

Samacheer Kalvi (TN State Board) Class 4 Science — Chapter 10, Air We Breathe. Composition and pollution of air. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 12 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1State the composition of air: Nitrogen ~78%, Oxygen ~21%, Argon ~0.9%, Carbon Dioxide ~0.04%, other gases and water vapour ~0.06%
2Demonstrate with experiments that air: occupies space, has weight, supports burning, is essential for life
3Explain that oxygen is needed for breathing and burning; nitrogen dilutes oxygen (too much oxygen would make fires uncontrollable)
4List 4 causes of air pollution: vehicle exhaust, factory smoke, burning of garbage/crop stubble, bursting firecrackers
5List 3 effects: respiratory diseases (asthma, bronchitis), acid rain, global warming
6Suggest 3 solutions: plant trees, use public transport/bicycle, say no to crackers, use cleaner fuels (CNG, LPG), stop burning garbage

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Why this chapter matters

Air We Breathe focuses on the most immediate environmental health issue: air quality. Class 4 children learn the exact composition of air (78% nitrogen, 21% oxygen, ~0.04% CO₂, etc.), understand that oxygen supports both breathing and burning, and — crucially — learn about air pollution: its causes (vehicles, factories, crackers, burning waste), its health effects (asthma, bronchitis, lung damage), and solutions (planting trees, using public transport, saying no to crackers). This chapter empowers children to demand clean air as a basic right.

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Air We Breathe — Class 4 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 4 Science, Chapter 10. Composition and pollution of air.

1. About this chapter

This chapter covers Air We Breathe as part of the Class 4 Samacheer Kalvi Science curriculum. It deals with composition and pollution of air and builds conceptual understanding essential for the TN School Term Exam.

By the end of this chapter, students will be able to:

Describe the composition of air
Explain causes and effects of air pollution

2. Key concepts

Concept 1: Describe the composition of air.
Concept 2: Explain causes and effects of air pollution.

3. Important terms and formulas

Term / Formula	Description
Describe the composition of…	Describe the composition of air
Explain causes and effects…	Explain causes and effects of air pollution

4. Worked examples

Example 1. Applying a key concept from this chapter.

Solution: Identify the relevant principle → apply the formula or rule → state the answer with correct units.

Example 2. A typical exam-style question on air we breathe.

Solution: Break the problem into steps, use the appropriate formula and verify the answer.

5. Common mistakes

Mistake: Skipping units or forgetting to state them. Fix: Always write units alongside every quantity and answer.
Mistake: Confusing similar terms or concepts in this chapter. Fix: Make a comparison table of the terms during revision.

6. Practice (exam-style)

Define the main term or principle covered in Chapter 10.
Give two real-life examples related to air we breathe.
Solve a short numerical or descriptive question from this chapter.
State one important formula and explain each symbol.

7. Answer key (hints)

Refer to section 2 (Key concepts) above for the definition.
Examples should be drawn from daily experience and local context.
Apply the formula from section 3, show all steps clearly.
Formula with units — refer to the textbook glossary for symbol meanings.

8. Quick revision

Class 4 Science — Chapter 10: Air We Breathe.
Core idea: Composition and pollution of air.
Key outcomes: Describe the composition of air; Explain causes and effects of air pollution.
Always revise diagrams / tables from the Samacheer Kalvi textbook before the exam.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Composition of air

Nitrogen (N₂) → ~78% — dilutes oxygen, essential for plant proteins. Oxygen (O₂) → ~21% — supports breathing and burning. Argon (Ar) → ~0.9%. Carbon Dioxide (CO₂) → ~0.04% — used by plants for photosynthesis. Other gases (neon, helium, methane, etc.) and water vapour → ~0.06%.

The oxygen percentage is exactly right for life. If oxygen were 25% or more, fires would burn uncontrollably and metals would rust much faster. If it were below 15%, most animals would suffocate. The balance is finely tuned.

Air pollution — PM2.5 and AQI

Major pollutants: PM2.5 and PM10 (tiny dust/soot particles that enter lungs and bloodstream), CO (carbon monoxide — from incomplete combustion, reduces blood's oxygen capacity), SO₂ and NO₂ (from factories and vehicles, cause acid rain). AQI (Air Quality Index) measures how polluted the air is: 0-50 = Good, 51-100 = Moderate, 101-200 = Unhealthy for sensitive groups, 200+ = Very unhealthy.

During Deepavali, the AQI in many Tamil Nadu cities spikes to 200-300+. A single hour of mass cracker bursting can pollute the air more than a month of normal vehicle emissions.

How to reduce air pollution

Individual actions: use bicycle or walk for short distances, use public transport, carpool, do not burn garbage or leaves, say no to firecrackers, plant and care for trees. Community/national actions: switch to electric vehicles, use solar and wind energy, enforce emission standards for factories, promote public transport (like Chennai Metro).

Chennai's Metro Rail has significantly reduced the number of cars on the road. One metro train can carry about 1000 passengers — replacing about 700 cars or 200 two-wheelers from the road.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Thinking oxygen is the main component of air (it is nitrogen)

✓ Oxygen is the MOST IMPORTANT gas for us, but it is NOT the most abundant. Nitrogen makes up 78% of the air. Oxygen is only 21%. Just because something is more important does not mean there is more of it.

WATCH OUT

✗ Thinking air is weightless

✓ Air has weight — about 1.2 kg per cubic metre at sea level. The total weight of Earth's atmosphere is about 5.5 quadrillion tonnes. The air pressure on your body right now is about 1 kg per square centimetre.

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