📘 Study MCQs
Q1. Phenolphthalein is a synthetic indicator. What color does it turn when added to a basic solution like sodium hydroxide?
A. Yellow
B. Red
C. Pink
D. Green
C. PinkPhenolphthalein is colorless in acidic and neutral solutions but turns pink to magenta in basic solutions, making it a widely used indicator for bases.
Q2. A student adds a few drops of phenolphthalein to a solution of hydrochloric acid. What color change will he observe?
A. Colorless to pink
B. Pink to colorless
C. Remains colorless
D. Colorless to red
C. Remains colorlessPhenolphthalein remains colorless in acidic solutions such as hydrochloric acid, as it does not change color in acidic or neutral conditions.
Q3. A student adds phenolphthalein to a colorless solution, and it turns pink. What is the nature of the solution?
A. Acidic
B. Neutral
C. Basic
D. Slightly sour
C. BasicA pink color with phenolphthalein indicates a basic solution, since the indicator only turns pink in the presence of bases.
Q4. Limewater is a basic solution. If a few drops of phenolphthalein are added to it, what will happen?
A. The solution will become colorless
B. The solution will turn pink
C. The solution will turn red
D. The solution will turn blue
B. The solution will turn pinkLimewater (calcium hydroxide solution) is basic, so it turns phenolphthalein pink.
Q5. Generally, acids have a specific taste. What is that taste?
A. Sweet
B. Bitter
C. Sour
D. Salty
C. SourAcids typically have a sour taste, as observed in lemon juice (citric acid), vinegar (acetic acid), and curd (lactic acid).
Q6. How do dilute acids generally feel when touched? (With a warning that this should never be tested directly)
A. Soapy and slippery
B. Sticky
C. No specific feeling
D. Watery
C. No specific feelingDilute acids do not have a characteristic feel like bases (which feel soapy); however, they can be corrosive and should never be touched directly.
Q7. Which gas is usually produced when an acid reacts with an active metal like zinc?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
C. HydrogenActive metals like zinc react with dilute acids to produce hydrogen gas, e.g., Zn + 2HCl → ZnCl₂ + H₂↑.
Q8. Acid rain is a environmental problem. What is the main cause of acid rain?
A. Excessive use of fertilizers
B. Burning of fossil fuels releasing oxides of sulphur and nitrogen
C. Deforestation
D. Use of air conditioners
B. Burning of fossil fuels releasing oxides of sulphur and nitrogenOxides of sulphur (SOâ‚‚) and nitrogen (NOâ‚“) from burning fossil fuels dissolve in rainwater to form sulphuric and nitric acids, causing acid rain.
Q9. What is the approximate pH of normal rain water?
A. Below 5.6
B. Around 5.6
C. Exactly 7
D. Above 8
B. Around 5.6Normal rainwater is slightly acidic (pH ~5.6) due to dissolved carbon dioxide forming carbonic acid, not due to pollution.
Q10. Acid rain can cause damage to buildings made of which material?
A. Wood
B. Plastic
C. Marble (Calcium carbonate)
D. Glass
C. Marble (Calcium carbonate)Acid rain reacts with calcium carbonate in marble, causing corrosion and deterioration, a process known as “marble cancer.”
Q11. What is the chemical process called when an acid and a base react to form salt and water?
A. Polymerization
B. Oxidation
C. Neutralization
D. Precipitation
C. NeutralizationNeutralization is the reaction between an acid and a base, producing salt and water: Acid + Base → Salt + Water.
Q12. A person suffers from indigestion due to excess acid in the stomach. What type of substance is taken to relieve this pain?
A. Acidic substance
B. Basic substance (antacid)
C. Neutral substance
D. Sour substance
B. Basic substance (antacid)Antacids are basic substances that neutralize excess stomach acid, providing relief from indigestion and heartburn.
Q13. Milk of Magnesia is often used as an antacid. Which base does it contain?
A. Sodium hydroxide
B. Calcium hydroxide
C. Magnesium hydroxide
D. Ammonium hydroxide
C. Magnesium hydroxideMilk of Magnesia is a suspension of magnesium hydroxide [Mg(OH)â‚‚], a mild base used to neutralize stomach acid.
Q14. Baking soda is a common home remedy for acidity. What is its chemical name?
A. Sodium chloride
B. Sodium carbonate
C. Sodium hydrogen carbonate
D. Calcium carbonate
C. Sodium hydrogen carbonateBaking soda is sodium hydrogen carbonate (NaHCO₃), a weak base that neutralizes excess acid and relieves indigestion.
Q15. Farmers add slaked lime to their fields. What is the purpose of this practice?
A. To add more acid to the soil
B. To make the soil more fertile by adding nutrients
C. To treat soil that is too acidic (basic soil treatment)
D. To kill insects
C. To treat soil that is too acidic (basic soil treatment)Slaked lime (calcium hydroxide) is a base that neutralizes acidic soil, raising the pH to a level suitable for crop growth.
Q16. Sometimes farmers add organic matter (compost) to the soil. This can also help treat soil that is too ______.
A. Basic (alkaline)
B. Sandy
C. Dry
D. Rocky
A. Basic (alkaline)Organic matter (compost) releases organic acids during decomposition, which helps neutralize alkaline soils.
Q17. Waste from factories is often acidic. Why is it dangerous to dump this waste directly into rivers?
A. It will change the color of the river
B. It will kill aquatic life by making the water acidic
C. It will make the river water salty
D. It will cause the river to freeze
B. It will kill aquatic life by making the water acidicAcidic waste lowers the pH of water bodies, harming or killing aquatic organisms that require a near-neutral pH to survive.
Q18. How is acidic factory waste treated before being released into water bodies?
A. By diluting it with large amounts of water
B. By adding a base to neutralize it
C. By boiling it
D. By filtering it
B. By adding a base to neutralize itAcidic waste is neutralized by adding a base (such as lime), converting it into a less harmful substance before disposal.
Q19. When an ant stings a person, it injects a liquid into the skin. What is the nature of this liquid?
A. Basic
B. Neutral
C. Acidic
D. Salty
C. AcidicAnt stings inject methanoic acid (formic acid), which causes pain and irritation.
Q20. What is a common household remedy to apply on an ant sting to get relief?
A. Lemon juice
B. Vinegar
C. Baking soda paste
D. Common salt
C. Baking soda pasteBaking soda (sodium hydrogen carbonate) is basic and neutralizes the formic acid from an ant sting, providing relief.
Q21. A bee sting is different from an ant sting. What is the nature of the liquid injected by a bee sting?
A. Acidic
B. Basic
C. Neutral
D. Sour
B. BasicBee venom is basic (alkaline) in nature, containing melittin and other basic compounds.
Q22. What can be used to treat a bee sting?
A. Baking soda paste
B. Lemon juice or vinegar
C. Soap solution
D. Sugar solution
B. Lemon juice or vinegarLemon juice or vinegar contains weak acids that neutralize the basic venom of a bee sting.
Q23. Why is it important to know whether a sting is from an ant or a bee before applying a remedy?
A. Because ants are more dangerous
B. Because one is acidic and the other is basic, so they need opposite treatments
C. Because the remedies smell different
D. Because the sting location is different
B. Because one is acidic and the other is basic, so they need opposite treatmentsAnt venom is acidic and requires a base for neutralization; bee venom is basic and requires an acid for neutralization.
Q24. In very hot weather, milk spoils quickly and becomes sour. Why does this happen?
A. The heat kills the bacteria
B. Bacteria convert the milk sugar (lactose) into lactic acid
C. The milk evaporates
D. The fat separates from the milk
B. Bacteria convert the milk sugar (lactose) into lactic acidLactic acid bacteria ferment lactose, producing lactic acid, which curdles milk and gives it a sour taste.
Q25. To preserve milk for a short period, especially in warm weather, people often boil it. Why does boiling help?
A. It adds nutrients to the milk
B. It kills the bacteria that turn milk sour
C. It makes the milk sweeter
D. It removes all the water
B. It kills the bacteria that turn milk sourBoiling kills most bacteria, including lactic acid bacteria, slowing down the spoilage process.
Q26. A student accidentally spills dilute hydrochloric acid on the laboratory floor. The teacher instructs her to neutralize it with a base. Which substance would be safest to use?
A. Concentrated sodium hydroxide
B. Water
C. Baking soda (sodium hydrogen carbonate)
D. Sulphuric acid
C. Baking soda (sodium hydrogen carbonate)Baking soda is a mild, safe base that neutralizes acids without the risk of strong exothermic reactions or corrosive hazards.
Q27. What will be the products when an acid reacts with a base in a neutralization reaction?
A. A new acid and a new base
B. Carbon dioxide and water
C. Salt and water
D. Hydrogen gas and salt
C. Salt and waterThe general neutralization reaction is: Acid + Base → Salt + Water.
Q28. Why is it not advisable to take antacid tablets regularly without a doctor’s advice?
A. They are too expensive
B. They can make the stomach too basic, affecting digestion
C. They taste bad
D. They are difficult to swallow
B. They can make the stomach too basic, affecting digestionOveruse of antacids can neutralize stomach acid excessively, impairing digestion and nutrient absorption.
Q29. Besides using a base, how can the effects of acid rain on a lake be reduced?
A. By adding more acid to the lake
B. By adding a basic substance like lime (calcium hydroxide) to the lake
C. By boiling the lake water
D. By filtering the lake water
B. By adding a basic substance like lime (calcium hydroxide) to the lakeAdding lime (calcium hydroxide) to an acidic lake neutralizes the acid, raising the pH to a level that supports aquatic life.
Q30. A solution turns phenolphthalein pink. When an acid is added to it drop by drop, what will happen to the pink color?
A. It will become darker pink
B. It will turn blue
C. It will become colorless
D. It will turn yellow
C. It will become colorlessAs acid is added to a basic solution, neutralization occurs. When the solution becomes neutral or acidic, phenolphthalein reverts to colorless.