Water is one of the most important and essential substances on Earth. It covers about 70% of the Earth’s surface and plays a vital role in supporting life. In 10th Class Chemistry Chapter 15 – Water, students learn about the physical and chemical properties of water, its role as a universal solvent, the difference between soft and hard water, water pollution, and waterborne infectious diseases.
This chapter is very important from the board examination point of view because it includes conceptual short questions, reasoning-based long questions, and important MCQs. Understanding the structure and properties of water helps students explain many natural processes, environmental issues, and health-related problems.
In these notes, you will find well-organized and exam-focused content including important MCQs, short questions, and detailed long questions to help you prepare effectively for your board exams. These notes are designed to make learning simple, clear, and result-oriented.
Important MCQs – Chapter 15 Water
1. What percentage of the human body consists of water?
(a) 50%
(b) 60%
(c) 70% ✅
(d) 80%
2. What percentage of the Earth’s water is suitable for drinking (potable)?
(a) 1%
(b) 0.2% ✅
(c) 2%
(d) 10%
3. What is the freezing point of pure water at sea level?
(a) 100°C
(b) 4°C
(c) 0°C ✅
(d) -1°C
4. What is one major disadvantage of hard water in boilers?
(a) Increases water level
(b) Reduces water pressure
(c) Forms scales which reduce efficiency ✅
(d) Produces too much steam
Short Questions – Chapter 15 Water
1. Why are non-polar compounds insoluble in water?
Answer:
Non-polar compounds are insoluble in water because they lack positive or negative poles. As a result, water molecules cannot form attractions or hydrogen bonds with them.
2. Differentiate between soft and hard water.
Answer:
-
Soft water: Produces lather with soap easily.
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Hard water: Does not produce lather with soap due to the presence of calcium and magnesium salts.
3. What is the difference between biodegradable and non-biodegradable substances?
Answer:
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Biodegradable substances: Can be broken down by microorganisms (e.g., food waste, paper).
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Non-biodegradable substances: Cannot be decomposed by microorganisms (e.g., plastics, detergents).
4. What is an industrial waste?
Answer:
Industrial waste is the leftover material from factories and industries, which includes toxic chemicals, heavy metals, acids, and oils that pollute water and the environment.
Long Questions – Chapter 15 Water
Q1: Explain the water pollution caused by industrial waste.
Answer:
Water pollution occurs when harmful substances are added to water bodies, making the water unfit for use. Industrial waste is one of the major contributors to water pollution.
What is Industrial Waste?
Industrial waste refers to toxic chemicals, sludge, oils, heavy metals, and non-biodegradable substances released by factories into water sources.
How Industrial Waste Causes Water Pollution:
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Discharge of Chemicals:
Factories often release toxic chemicals like mercury, lead, arsenic, and acids into rivers and lakes.
➡ These chemicals harm aquatic life and contaminate drinking water. -
Thermal Pollution:
Some industries release hot water used in cooling processes into rivers.
➡ This increases water temperature, reduces dissolved oxygen, and kills fish and aquatic plants. -
Oil Spillage:
Oil industries may spill oil and grease into nearby water bodies.
➡ Oil forms a layer on the surface, blocking oxygen supply to aquatic organisms. -
Plastic and Non-Biodegradable Waste:
Industries also dump plastics and synthetic materials into water.
➡ These materials do not decompose and remain in the environment for years.
Summary:
Industrial waste seriously pollutes water, causing harm to the environment, aquatic life, and human health. Proper waste treatment and strict pollution laws are essential to protect water resources.
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