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Q1. Calcium hydroxide is written as:
Calcium hydroxide is formed when calcium oxide (quick lime) reacts with water. Its chemical formula is Ca(OH)₂. It has one calcium ion (Ca²⁺) and two hydroxide ions (OH⁻). CaCO₃ is calcium carbonate (limestone/marble), CaCl₂ is calcium chloride, and CaO is calcium oxide (quick lime). So Ca(OH)₂ is correct.
Q2. Which of the following is an acid?
HCl is hydrochloric acid — it is an acid. NaOH (sodium hydroxide), Ca(OH)₂ (calcium hydroxide), and NH₄OH (ammonium hydroxide) are all bases. Acids have a sour taste, turn blue litmus red, and contain hydrogen ions (H⁺) in solution. So HCl is correct.
Q3. Which indicator works by smell change?
Onion is an olfactory indicator — it works by a change in smell. The characteristic smell of onion disappears in a basic solution but remains in an acidic solution. Methyl orange, litmus, and turmeric are colour-change indicators, not smell-change indicators. So onion is correct.
Q4. Acids and bases neutralise each other because:
Acids and bases neutralise each other because the H⁺ ions from the acid combine with the OH⁻ ions from the base to form water (H₂O). This cancels the acidic and basic properties of both. The products are salt and water. Dissolving, violent reaction, and gas formation are not the reason for neutralisation. So they cancel each other’s properties is correct.
Q5. Magnesium hydroxide is represented as:
Magnesium hydroxide has one magnesium ion (Mg²⁺) and two hydroxide ions (OH⁻), so its formula is Mg(OH)₂. It is an antacid (milk of magnesia). MgO is magnesium oxide, MgCl₂ is magnesium chloride, MgSO₄ is magnesium sulphate. So Mg(OH)₂ is correct.
Q6. Acids and bases cancel each other’s effect by the process of:
The process by which acids and bases cancel each other’s effects is called neutralisation. In this reaction, an acid reacts with a base to form salt and water. Reduction is gain of electrons, oxidation is loss of electrons, and displacement is one element replacing another. So neutralisation is correct.
Q7. Which substance is used as an olfactory indicator?
Vanilla essence is an olfactory indicator — its smell disappears in a basic solution but remains in an acidic solution. Phenolphthalein, methyl orange, and litmus are colour-change indicators, not smell indicators. So vanilla essence is correct.
Q8. The colour of neutral litmus solution is:
Litmus solution is naturally purple in colour in a neutral solution. It turns red in acidic solutions and blue in basic solutions. The purple colour is the neutral state. Green and yellow are not litmus colours. So purple is correct.
Q9. Acids generally have:
Acids generally have a sour taste. For example, citric acid in lemons gives a sour taste, acetic acid in vinegar tastes sour. Bases have a bitter taste and soapy feel. Salty taste comes from salts, sweet taste from sugars. So sour taste is correct.
Q10. Indicators tell whether a substance is acidic or basic by:
Indicators are substances that change colour in acidic or basic media. For example, litmus turns red in acid and blue in base. Taste and smell are not used for safety reasons (toxic substances). Temperature change is not a property of indicators. So colour change is correct.
Q11. Litmus is a:
Litmus is a natural indicator. It is extracted from lichens (plant-like organisms). It is not a salt, not synthetic (though it can be made artificially, it is originally natural), and not an olfactory indicator (it changes colour, not smell). So natural indicator is correct.
Q12. Bitter taste in food is due to the presence of:
Bases generally have a bitter taste and a soapy feel. For example, baking soda (sodium bicarbonate) tastes slightly bitter. Acids have sour taste, salts have salty taste, sugars have sweet taste. So bitter taste is due to bases.
Q13. Clove oil can act as a/an:
Clove oil is an olfactory indicator — its smell changes in acidic and basic media. It is not a base, acid, or salt. So olfactory indicator is correct.
Q14. Natural substances that indicate acids or bases are called:
Natural substances that change colour or smell in acidic or basic solutions are called indicators. Examples include litmus, turmeric, red cabbage, and onion. Catalysts speed up reactions, reagents are substances used in reactions, electrolytes conduct electricity. So indicators is correct.
Q15. Litmus solution is naturally:
Litmus solution in its natural, neutral state is purple in colour. It is extracted from lichens and is purple. It turns red in acidic solutions and blue in basic solutions. So purple is correct.
Q16. Red litmus paper turns blue in:
Red litmus paper turns blue when it comes into contact with a basic (alkaline) solution. It turns red in acidic solution (but it is already red). In neutral solution, it stays red. Salt solution may be neutral depending on the salt. So basic solution is correct.
Q17. The cloth strips soaked with onion are used to test:
Cloth strips soaked with onion are used as an olfactory indicator to test acids and bases. The smell of onion disappears in a basic solution but remains in an acidic solution. They are not used to test gases, metals, or salts. So acids and bases is correct.
Q18. Which indicator is purple in neutral solution?
Litmus is purple in neutral solution. Phenolphthalein is colourless in neutral/acidic solution and pink in basic. Methyl orange is orange/yellow in neutral. Turmeric is yellow in neutral/acidic and reddish-brown in basic. So litmus is correct.
Q19. Litmus solution is extracted from:
Litmus is a natural dye extracted from lichens, which are symbiotic organisms (fungus + algae). Moss, algae, and fungus alone are not used to extract litmus. So lichen is correct.
Q20. Distilled water is:
Distilled water is neutral — it has neither acidic nor basic properties. It contains equal concentrations of H⁺ and OH⁻ ions. It does not change the colour of litmus. So neutral is correct.
Q21. Lichen belongs to the division:
Lichen is a symbiotic association of algae and fungi. It belongs to the division Thallophyta (plant body is not differentiated into root, stem, and leaves). Angiosperms are flowering plants, Bryophyta are mosses, Pteridophyta are ferns. So Thallophyta is correct.
Q22. Onion smell disappears in:
The characteristic smell of onion disappears in a basic solution. This is because the chemical responsible for the smell reacts with the base. In acidic or neutral solutions, the smell remains. So basic solution is correct.
Q23. Ammonium hydroxide has the formula:
Ammonium hydroxide is formed when ammonia gas (NH₃) dissolves in water. Its formula is NH₄OH. NaOH is sodium hydroxide, NH₄Cl is ammonium chloride, NH₃ is ammonia. So NH₄OH is correct.
Q24. Which flower petals can act as natural indicators?
The petals of flowers like Hydrangea, Petunia, and Geranium contain pigments that change colour in acidic or basic solutions. They can act as natural indicators. Lotus, sunflower, and rose are not commonly used as indicators. So Hydrangea, Petunia, Geranium is correct.
Q25. A curry stain turns reddish-brown when scrubbed with soap because soap is:
Turmeric (present in curry) is a natural indicator that is yellow in neutral/acidic medium and turns reddish-brown in basic medium. Since soap is basic in nature, the curry stain turns reddish-brown when scrubbed with soap. So soap is basic is correct.
Q26. Which of the following is the correct remedy for acidity after overeating?
Acidity is caused by excess acid in the stomach. Baking soda (sodium bicarbonate) is a base that neutralises the excess acid. Fruit juice, lemon juice, and vinegar are acidic and would make acidity worse. So baking soda solution is correct.
Q27. Which of the following is a base?
NaOH (sodium hydroxide) is a base. HNO₃ (nitric acid), H₂SO₄ (sulphuric acid), and CH₃COOH (acetic acid) are all acids. Bases have bitter taste, soapy feel, and turn red litmus blue. So NaOH is correct.
Q28. If red litmus shows no change, the solution may be:
Red litmus paper remains red in acidic and neutral solutions. It only turns blue in basic solutions. If there is no change, the solution could be acidic (but red litmus is already red, so no change would be seen) OR neutral. However, since acidic is already red, the best answer is neutral because acidic would also show no change. But if the solution were acidic, red litmus would stay red. So the correct interpretation is that it could be neutral (or acidic). Among the options, neutral is the most appropriate.
Q29. Sour taste in food is due to the presence of:
Sour taste in food is due to the presence of acids. For example, citric acid in lemons, acetic acid in vinegar, lactic acid in sour milk. Bases have bitter taste, alcohols do not taste sour, salts have salty taste. So acids is correct.
Q30. Baking soda solution is used as a remedy because it is:
Baking soda solution is basic in nature. It neutralises excess acid in the stomach, providing relief from acidity. Salty, neutral, and acidic are incorrect. So basic is correct.
Q31. Substances whose odour changes in acidic or basic media are called:
Olfactory indicators are substances whose smell (odour) changes in acidic or basic media. Examples include onion, vanilla, and clove oil. Synthetic indicators (like phenolphthalein) change colour. Natural indicators (like litmus) change colour. So olfactory indicators is correct.
Q32. Bases change red litmus to:
Bases turn red litmus paper blue. This is a characteristic test for bases. Acids turn blue litmus red. So blue is correct.
Q33. The smell of vanilla essence disappears in:
Vanilla essence is an olfactory indicator — its smell disappears in a basic solution but remains in an acidic solution. So the smell disappears in base.
Q34. To test acids and bases in lab, substances are placed on:
In laboratory activities, small amounts of substances to be tested with indicators are usually placed on a watch glass. This allows easy observation of colour change. Test tubes, beakers, and conical flasks are used for larger quantities or reactions. So watch glass is correct.
Q35. Indicators help us identify whether a substance is:
Indicators are used to determine whether a substance is acidic, basic, or neutral. They do not identify weight, physical state, or metallic nature. So acidic or basic is correct.
Q36. Turmeric is an example of a:
Turmeric is a natural indicator obtained from the turmeric plant. It is yellow in neutral/acidic medium and turns reddish-brown in basic medium. It is not an olfactory indicator (it does not change smell), not a synthetic indicator (it is natural), and not a neutral substance (it indicates pH). So natural indicator is correct.
Q37. Phenolphthalein remains colourless in:
Phenolphthalein is a synthetic indicator that remains colourless in acidic solutions. In basic solutions, it turns pink. In neutral solutions, it is colourless too, but the standard test for acids is that it remains colourless. So acidic solution is the best answer.
Q38. Which is NOT an indicator?
Sugar is a sweet-tasting substance and does not change colour or smell in acidic or basic media — it is not an indicator. Phenolphthalein, litmus, and turmeric are all indicators. So sugar is NOT an indicator.
Q39. Red cabbage leaves can act as:
Red cabbage contains pigments (anthocyanins) that change colour in acidic and basic solutions. It can be used as a natural indicator. It is not a catalyst, salt, or fertiliser. So indicators is correct.
Q40. Neutralisation is useful in treating:
Neutralisation is used to treat acidity (excess acid in the stomach). Antacids like milk of magnesia (a base) neutralise the excess stomach acid. Infections are treated with antibiotics, fractures with immobilisation, and burns with cooling or ointments. So acidity is correct.
Q41. Bases generally have:
Bases generally have a bitter taste and a soapy feel. For example, baking soda has a slightly bitter taste. Acids have sour taste, salts have salty taste, sugars have sweet taste. So bitter taste is correct.
Q42. Another synthetic indicator used to test acids and bases is:
Methyl orange is a synthetic indicator. It turns red in acidic solutions and yellow in basic solutions. Red cabbage, clove oil, and turmeric are natural indicators. So methyl orange is correct.
Q43. Which of the following is a synthetic indicator?
Phenolphthalein is a synthetic indicator (man-made in a laboratory). Onion, litmus, and turmeric are natural indicators. So phenolphthalein is correct.
Q44. Onion strips are stored overnight in a fridge to:
Onion strips are soaked in water and stored in a fridge overnight to prepare an onion extract that can be used as an olfactory indicator. This allows the odour to be released into the water. Drying, removing smell, or absorbing odour are not the purposes. So prepare indicator is correct.
Q45. Acetic acid is represented by the formula:
Acetic acid (present in vinegar) has the formula CH₃COOH (or C₂H₄O₂). H₂SO₄ is sulphuric acid, HNO₃ is nitric acid, HCl is hydrochloric acid. So CH₃COOH is correct.
Q46. Soap is basic in nature because it:
Soap is basic in nature. This can be tested using turmeric — turmeric turns reddish-brown in basic solutions. It does not smell sour (that’s acidic), bases are bitter but we don’t taste soap for safety, and bases turn red litmus blue (not blue litmus red — that’s acids). So turns turmeric reddish-brown is correct.
Q47. Methyl orange turns red in:
Methyl orange is a synthetic indicator that turns red in acidic solutions and yellow in basic solutions. It remains orange in neutral solutions. So acid is correct.
Q48. The reddish-brown turmeric stain turns yellow again after washing with water because:
A curry stain (turmeric) turns reddish-brown when soap (basic) is applied. When washed with water, the excess soap (base) is removed, and the turmeric returns to its yellow colour because water is neutral and turmeric is yellow in neutral medium. Water is not basic or acidic, turmeric does not dissolve completely, so the removal of excess base is correct.
Q49. Onion can be used as a:
Onion is an olfactory indicator because its smell changes in acidic and basic media. It is a natural indicator (since it comes from nature), but the more specific classification is olfactory indicator because it works by smell, not colour. So olfactory indicator is the best answer.
Q50. Acids change blue litmus to:
Acids turn blue litmus paper red. This is a characteristic test for acids. Bases turn red litmus blue. So red is correct.