**Air Composition:** Nitrogen 78%, Oxygen 21%, Argon and other gases 1%. **Key Point:** We need oxygen to survive — can't live without it for more than a few minutes. Moving air is called wind.
**Water Facts:** Two-thirds of Earth is water, but 97% is saltwater (oceans). Only 3% is freshwater, and most of that is frozen in ice sheets or underground — very hard to reach. Only freshwater from rivers, lakes, and wells is easily accessible.
**Uses of Water:** Drinking, cooking, bathing, washing, growing crops, industrial use.
**Water Wastage:** Happens when taps run without use, leaks in pipes, long showers. **Ways to Save:** Turn off taps, fix leaks, recycle water, harvest rainwater.
**Water Pollution:** Caused by throwing trash and waste from homes and factories into water sources.
**Windmill:** Uses wind energy to rotate and can generate electricity. Examples in India: Muppandal (Tamil Nadu), Jaisalmer (Rajasthan), Brahmanvel (Maharashtra).
**Diagrams to Remember:** Composition of air pie chart showing 78-21-1 split; water cycle showing freshwater sources.
**Don't Confuse:** Wind ≠ Air (wind is moving air); Saltwater ≠ Freshwater (salt vs fresh); Wastage ≠ Pollution (lost vs made dirty).
Q1. What percentage of air is nitrogen?
Answer: A — According to the composition of air shown in the chapter, nitrogen makes up 78 out of every 100 parts of air.
Q2. Why do we need oxygen?
Answer: B — The chapter states that oxygen in the air we breathe is essential for our body to perform its functions and for our survival.
Q3. What is moving air called?
Answer: C — The chapter defines moving air as wind, which can blow fast during a storm or gently as a breeze.
Q4. Which of these is NOT a source of freshwater?
Answer: C — Oceans contain saltwater, not freshwater; rivers, lakes, and wells contain freshwater that we can use.
Q5. Fill in the blank: A __________ is an area with many windmills that generate electricity.
Answer: A — The chapter defines a windmill farm as an area with a large number of windmills that use wind energy to generate electricity.
Q6. If you turn off the tap while brushing your teeth, what will happen?
Answer: B — Turning off taps when not in use is one of the ways to reduce water wastage as mentioned in Activity 11.3.
Q7. Looking at the air composition diagram, what does the largest section represent?
Answer: B — In Fig. 11.1, nitrogen occupies 78 out of 100 squares, making it the largest section of air composition.
Q8. Which statement correctly explains why freshwater is precious?
Answer: B — The chapter explains that water covers two-thirds of Earth but most is saltwater, and freshwater that is easily accessible is found in limited amounts in ponds, rivers, lakes, and wells.
Q9. How does a firki help us understand air?
Answer: B — Activity 11.2 shows that when you blow air on a firki or move it through air, it rotates because wind (moving air) pushes it.
Q10. What is the main cause of water pollution mentioned in the chapter?
Answer: B — The chapter clearly states that we pollute freshwater by throwing trash and waste from homes and industries into water sources like rivers and lakes.
What percentage of air is oxygen?
Oxygen makes up 21% of the air we breathe.
Why can't we hold our breath for a long time?
Our body needs oxygen to function, and holding breath stops oxygen from entering our lungs.
What is wind?
Wind is air that is moving from one place to another.
How does a firki work?
Wind pushes the folded paper wings of a firki, making it spin around.
What percentage of Earth's water is saltwater?
About two-thirds of Earth is covered in water, and most of it is salty ocean water.
Why is freshwater precious?
Freshwater is precious because only a small amount is easily available for drinking and farming, while most of Earth's water is salty.
Name three uses of water in daily life.
Water is used for drinking, cooking, bathing, washing, cleaning, and growing crops.
What is a windmill farm?
A windmill farm is an area with many windmills that use wind energy to generate electricity.
How does water get polluted?
Water becomes polluted when trash, waste from homes, and waste from industries are dumped into rivers, lakes, and other water sources.
What are two ways to reduce water wastage?
We can reduce water wastage by turning off taps when not using them and fixing water leaks quickly.
What is the main gas in air that we need to survive? [1 mark]
Look at the composition of air (Fig. 11.1) — it's not nitrogen (78%) or argon. Remember Activity 11.1 where you held your breath.
Name any two uses of water in daily life and explain why water is precious. [2 marks]
Water is used for drinking, cooking, bathing, washing, and crops. Water is precious because most of Earth's water is salty and only small amounts of freshwater are easily available.
Explain with an example from daily life how water is wasted at home. How can this wastage be reduced? [3 marks]
Choose any activity from Table 11.1 like hand washing, brushing teeth, or showering. Explain how water runs without being used. Give one way to reduce it like turning off taps or fixing leaks.
Describe how a windmill works and explain how windmill farms in India help us. Draw and label a simple diagram of a windmill. [5 marks]
Wind moves and rotates the wings of a windmill. This rotation can generate electricity. Name Indian windmill farms like Muppandal (Tamil Nadu) or Jaisalmer (Rajasthan). Draw a windmill with blades/wings and label them.
True or False: Saltwater from oceans can be used directly for drinking and farming. Give a reason for your answer. [2 marks]
This is False. Saltwater is not fit for drinking, agriculture, or industry. We need freshwater from rivers, lakes, wells, and underground sources.
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