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Tamil Nadu (TNBSE)Class 3 Science★ 5-6 marks in TN Class 3 Term 3 exams — properties of air, uses of air, air pollution, and short written answers

Air

Samacheer Kalvi (TN State Board) Class 3 Science — Chapter 10, Air. Composition and importance of air. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 10 min readEasy difficulty✓ Free · NCERT-aligned

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

1State properties of air: colourless, odourless, tasteless, occupies space, has weight, exerts pressure
2Describe simple experiments proving air occupies space (inverted glass in water — water does not enter) and has weight (inflated balloon weighs more than deflated)
3State that air is a mixture of gases, mainly nitrogen (78%) and oxygen (21%), with small amounts of CO₂, argon, and others
4List at least 4 uses of air: breathing, burning (oxygen needed for fire), flying kites and windmills, dispersing seeds and pollen
5Define wind as moving air and differentiate between breeze (gentle), wind (stronger), and storm/gale (very strong, destructive)
6Identify causes of air pollution: smoke from vehicles and factories, burning garbage and crop stubble, dust from construction, bursting crackers
7Suggest 2 ways to reduce air pollution: plant trees, use bicycles or public transport, say no to crackers

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Why this chapter matters

Air is invisible, yet it is all around us and essential for life. This chapter makes the invisible visible — through experiments that prove air occupies space (an inverted glass in water), has weight (a deflated vs inflated balloon), and exerts pressure. Children learn that air is a mixture of gases (mostly nitrogen and oxygen), that oxygen supports burning and breathing, and that moving air is wind — from a gentle breeze to a powerful storm. The chapter ends with air pollution: what causes it, how it harms us, and what we can do.

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Air — Class 3 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 3 Science, Chapter 10. Composition and importance of air.

1. About this chapter

This chapter covers Air as part of the Class 3 Samacheer Kalvi Science curriculum. It deals with composition and importance of air and builds conceptual understanding essential for the TN School Term Exam.

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

List the components of air
Explain the importance of clean air for life

2. Key concepts

Concept 1: List the components of air.
Concept 2: Explain the importance of clean air for life.

3. Important terms and formulas

Term / Formula	Description
List the components of…	List the components of air
Explain the importance of…	Explain the importance of clean air for life

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.

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.
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 3 Science — Chapter 10: Air.
Core idea: Composition and importance of air.
Key outcomes: List the components of air; Explain the importance of clean air for life.
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.

Properties of air

Colourless → you cannot see air. Odourless → pure air has no smell (if you smell something, that is an impurity, not air itself). Tasteless → air has no taste. Occupies space → take an empty bottle, dip it upside down in water; water does not enter because air occupies the space inside. Has weight → an inflated balloon is heavier than a deflated one. Exerts pressure → when you suck through a straw, air pressure pushes the liquid up.

These properties can be demonstrated with simple experiments at home. Try the inverted glass experiment or weigh balloons to see air's weight.

Composition of air

Air is a mixture of gases: Nitrogen (N₂) → ~78%. Oxygen (O₂) → ~21%. Argon → ~0.9%. Carbon dioxide (CO₂) → ~0.04%. Other gases and water vapour → trace amounts.

Oxygen is the most important component for us — it supports breathing and burning. When you inhale, your body takes oxygen from the air. When you exhale, you release carbon dioxide.

Uses of air

Breathing → all living things need oxygen from air (fish use dissolved oxygen in water). Burning → oxygen supports combustion; without air, a fire goes out. Wind energy → windmills convert moving air into electricity. Flight → birds, aeroplanes, and kites fly using air. Seed dispersal → wind carries seeds (like dandelion, cotton) to new places. Pollination → wind carries pollen from one flower to another.

Try covering a burning candle with a glass. When the oxygen inside the glass is used up, the candle goes out. This proves air (specifically oxygen) is needed for burning.

Air pollution

Causes → vehicle exhaust, factory smoke, burning garbage/leaves/crop stubble, construction dust, bursting firecrackers, use of coal and wood for cooking. Effects → breathing problems (asthma, bronchitis), eye irritation, acid rain (harms crops and buildings), global warming. Solutions → plant more trees (trees absorb CO₂ and release O₂), use bicycles or public transport, avoid bursting crackers, use cleaner fuels (CNG, LPG), stop burning garbage.

Delhi's air quality becomes dangerously poor every winter — mainly due to vehicle emissions and crop stubble burning. Children in Delhi are sometimes advised to wear masks. Clean air is a basic right.

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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 air is 'nothing' — just empty space

✓ Air is matter — it is made of gas molecules (mainly nitrogen and oxygen). It occupies space, has weight, and exerts pressure. An 'empty' bottle is actually full of air!

WATCH OUT

✗ Thinking we breathe in oxygen and breathe out only carbon dioxide

✓ We breathe in air that is ~21% oxygen. We breathe out air that still has ~16% oxygen and ~4% CO₂. We use only about 5% of the oxygen we inhale. That is why mouth-to-mouth resuscitation works — the exhaled air still has plenty of oxygen.

WATCH OUT

✗ Calling all moving air 'wind'

✓ Gentle moving air → breeze. Strong moving air → wind. Very strong destructive moving air → storm, gale, or cyclone. Different speeds, different names.

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