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Substances in Daily Use & Applied Chemistry — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Substances in Daily Use & Applied Chemistry MCQs with step-by-step solutions covering Soaps & Detergents, Polymers, Glass, Fertilizers, Air Composition, Water Purification. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Soaps & Detergents · easy · theory
Chemically, an ordinary bath soap is best described as
A. a long-chain alcohol dissolved in water
B. a simple sugar dissolved in oil
C. the sodium or potassium salt of a long-chain fatty acid ✓ Correct
D. the sodium salt of a strong mineral acid
Solution: Soap is made by heating fats or oils with sodium (or potassium) hydroxide. The product is the sodium or potassium salt of long-chain fatty acids. This reaction is called saponification.
Q2 — Polymers · easy · theory
A polymer such as polythene is best described as a
A. very large molecule built from many small repeating units joined together ✓ Correct
B. single tiny molecule that cannot be broken down any further
C. mixture of two different metals melted together
D. salt formed by the reaction of an acid with a base
Solution: A polymer is a giant molecule made by joining a very large number of small repeating units called monomers. Polythene, for instance, is formed by linking many ethene molecules together.
Q3 — Glass · easy · theory
The chief raw material used in making ordinary glass is
A. common salt
B. washing soda alone
C. graphite
D. sand (silica) ✓ Correct
Solution: Ordinary glass is made mainly from sand, which is silica (SiO2), melted together with soda (sodium carbonate) and limestone (calcium carbonate) at a high temperature.
Q4 — Fertilizers · easy · theory
The three main nutrient elements supplied to crops by chemical fertilizers are
A. carbon, hydrogen and oxygen
B. sodium, chlorine and calcium
C. iron, copper and zinc
D. nitrogen, phosphorus and potassium ✓ Correct
Solution: The three major nutrients that fertilizers provide are nitrogen (N), phosphorus (P) and potassium (K), together written as NPK. Plants obtain carbon, hydrogen and oxygen from air and water.
Q5 — Air Composition · easy · theory
By volume, the most abundant gas in clean, dry air is
A. argon
B. carbon dioxide
C. oxygen
D. nitrogen ✓ Correct
Solution: Clean dry air is about 78 percent nitrogen and about 21 percent oxygen by volume. Nitrogen is therefore the most abundant gas in air, while carbon dioxide and argon are present in much smaller amounts.
Q6 — Water Purification · easy · theory
At a municipal water works, a small amount of chlorine is added to the water mainly to
A. increase the hardness of the water
B. change the colour of the water
C. kill the disease-causing germs present in the water ✓ Correct
D. give the water a sweeter taste
Solution: Chlorine is added as a disinfectant. It kills bacteria and other disease-causing microbes, making the water safe to drink. This step is known as chlorination.
Q7 — Soaps & Detergents · hard · theory
Soap molecules remove oily dirt by forming tiny clusters called:
A. polymers
B. ions
C. micelles ✓ Correct
D. crystals
Solution: The soap tails dissolve in oil while the heads face water, forming micelles that lift dirt away.
Q8 — Soaps & Detergents · hard · theory
Soaps do not form a good lather with hard water because hard water contains:
A. excess soap
B. no minerals
C. calcium and magnesium salts ✓ Correct
D. only sodium salts
Solution: Ca²⁺ and Mg²⁺ ions react with soap to form an insoluble scum, so little lather forms.
Q9 — Soaps & Detergents · hard · theory
The process of making soap by reacting fats/oils with an alkali is called:
A. saponification ✓ Correct
B. neutralisation
C. polymerisation
D. fermentation
Solution: Saponification is the alkaline hydrolysis of fats/oils to produce soap and glycerol.
Q10 — Polymers · hard · theory
Which of the following is a natural polymer?
A. Nylon
B. Polythene
C. Cellulose ✓ Correct
D. PVC
Solution: Cellulose (in plants) is a natural polymer; the others are synthetic.
Q11 — Polymers · hard · theory
Plastics cause serious environmental problems mainly because they are:
A. easily burnt safely
B. natural
C. very expensive
D. non-biodegradable ✓ Correct
Solution: Most plastics are non-biodegradable, so they persist in the environment for a very long time.
Q12 — Glass · hard · theory
Glass is best described as a(n):
A. liquid
B. amorphous solid ✓ Correct
C. crystalline solid
D. gas
Solution: Glass lacks a regular crystal structure, so it is an amorphous (non-crystalline) solid.
Q13 — Glass · hard · theory
Toughened (safety) glass used in car windows is designed to:
A. break into small blunt pieces instead of sharp shards ✓ Correct
B. bend like rubber
C. conduct electricity
D. never break
Solution: Safety glass crumbles into small, relatively harmless granules, reducing injury.
Q14 — Fertilizers · hard · theory
Excessive use of chemical fertilizers can pollute water bodies and cause:
A. purer water
B. less algae
C. no effect
D. eutrophication (excess algal growth) ✓ Correct
Solution: Fertilizer run-off enriches water with nutrients, causing algal blooms (eutrophication) that harm aquatic life.
Q15 — Fertilizers · hard · theory
Fertilizers differ from manure in that fertilizers are:
A. always organic
B. free of nutrients
C. made from decomposed plant/animal waste
D. manufactured chemicals rich in specific nutrients ✓ Correct
Solution: Fertilizers are industrially produced and nutrient-specific, unlike organic manure.
Q16 — Air Composition · hard · theory
The approximate percentage of carbon dioxide in normal air is:
A. about 21%
B. about 10%
C. about 78%
D. about 0.04% ✓ Correct
Solution: CO₂ is a minor component, only about 0.03–0.04% of the air.
Q17 — Air Composition · hard · theory
The most abundant noble gas present in air is:
A. neon
B. krypton
C. helium
D. argon ✓ Correct
Solution: Argon makes up about 0.9% of the atmosphere — the most abundant noble gas in air.
Q18 — Water Purification · hard · theory
Chlorine is added to drinking water in a treatment plant mainly to:
A. add taste
B. kill disease-causing germs ✓ Correct
C. increase hardness
D. remove colour only
Solution: Chlorination disinfects water by killing bacteria and other pathogens.
Q19 — Water Purification · hard · theory
Reverse osmosis (RO) purifiers are used mainly to remove:
A. dissolved salts and impurities ✓ Correct
B. only large solid particles
C. only colour
D. oxygen
Solution: RO forces water through a semipermeable membrane, removing dissolved salts and fine impurities.
Q20 — Soaps & Detergents · hard · theory
Assertion: Synthetic detergents can be used for washing even in hard water. Reason: The calcium and magnesium salts of detergents are soluble in water. Choose the correct option.
A. The assertion is false but the reason is true
B. The assertion is true but the reason is false
C. Both assertion and reason are true, and the reason correctly explains the assertion ✓ Correct
D. Both assertion and reason are true, but the reason does not explain the assertion
Solution: Unlike soaps, detergents form calcium and magnesium salts that stay soluble, so they do not form scum and keep lathering and cleaning in hard water. The reason therefore correctly explains the assertion.
Q21 — Polymers · hard · numerical
A sample of polythene has an average molar mass of 28000 g/mol. If it is built from ethene units of molar mass 28 g/mol, the average number of ethene units in one polythene molecule is about
A. 100
B. 28000
C. 1000 ✓ Correct
D. 280
Solution: Number of repeating units = molar mass of the polymer divided by the molar mass of one monomer = 28000 / 28 = 1000. So about 1000 ethene units join to form each polythene molecule.
Q22 — Glass · hard · theory
Laboratory beakers and ovenware are made from borosilicate (Pyrex-type) glass rather than ordinary glass because borosilicate glass
A. dissolves slowly and safely in hot water
B. is an excellent conductor of heat and electricity
C. melts at a much lower temperature than ordinary glass
D. expands very little on heating and so resists cracking when the temperature changes suddenly ✓ Correct
Solution: Adding boron oxide gives borosilicate glass a very low thermal expansion. It barely expands or contracts when heated or cooled quickly, so it does not crack under sudden temperature change, making it suitable for laboratory and oven use.
Q23 — Fertilizers · hard · numerical
Urea has the formula CO(NH2)2 and a molar mass of 60 g/mol. It contains two nitrogen atoms, each of atomic mass 14. The percentage of nitrogen by mass in urea is about
A. 35 percent
B. 60 percent
C. 47 percent ✓ Correct
D. 23 percent
Solution: Mass of nitrogen in one formula unit = 2 × 14 = 28. Percentage of nitrogen = (28 / 60) × 100, which is about 46.7 percent, that is roughly 47 percent. This high nitrogen content makes urea a very effective nitrogen fertilizer.
Q24 — Air Composition · hard · numerical
Air contains roughly 21 percent oxygen by volume. What volume of oxygen is present in 500 litres of air?
A. 42 litres
B. 210 litres
C. 21 litres
D. 105 litres ✓ Correct
Solution: Volume of oxygen = 21 percent of 500 = (21 / 100) × 500 = 105 litres. So about 105 litres of the 500 litres of air is oxygen.
Q25 — Water Purification · hard · theory
A sample of muddy water is passed through a cloth filter and then boiled. Which impurity is still most likely to remain in it?
A. dissolved common salt ✓ Correct
B. floating leaves
C. large grains of sand
D. suspended mud particles
Solution: Filtering removes suspended solids such as sand, mud and leaves, and boiling kills germs, but neither of these removes dissolved salts. Common salt stays dissolved and can be separated only by methods like distillation or reverse osmosis.
Q26 — Soaps & Detergents · medium · theory
Soap is chemically the sodium or potassium salt of:
A. nitric acid
B. carbonic acid
C. long-chain fatty acids ✓ Correct
D. mineral acids
Solution: Soaps are sodium/potassium salts of long-chain fatty acids.
Q27 — Soaps & Detergents · medium · theory
Detergents are preferred over soaps for washing in hard water because detergents:
A. form scum in hard water
B. do not clean
C. dissolve only in oil
D. work well even in hard water ✓ Correct
Solution: Detergents do not form scum with hard-water ions, so they clean effectively in hard water.
Q28 — Polymers · medium · theory
A polymer is a very large molecule made of many small repeating units called:
A. isotopes
B. ions
C. atoms only
D. monomers ✓ Correct
Solution: Polymers are formed by joining many small monomer units together.
Q29 — Polymers · medium · theory
Which of the following is a synthetic polymer?
A. Cotton
B. Nylon ✓ Correct
C. Wool
D. Silk
Solution: Nylon is a man-made (synthetic) polymer; cotton, silk and wool are natural.
Q30 — Polymers · medium · theory
A common plastic used to make bags and bottles is:
A. polythene ✓ Correct
B. bakelite only
C. rubber
D. nylon only
Solution: Polythene (polyethylene) is widely used for bags, bottles and packaging.