Acids, Bases and Salts · Class 10 Science: 216 MCQs with answers

Q1. An acid turns ______ litmus ______.

Q2. Acid + base → salt + water is called:

Q3. The acid present in vinegar is:

Q4. What are indicators? Name two synthetic indicators with their colours in acid and base.

Q5. What are olfactory indicators? Explain with an example why they are useful.

Q6. Describe the reaction of zinc with dilute sulphuric acid, and the test for the gas evolved.

Q7. What happens when sodium carbonate reacts with dilute hydrochloric acid? Give the equation and the gas test.

Q8. Define neutralisation and give two applications from daily life.

Q9. Acid solutions conduct electricity because they contain:

Q10. Which solution will NOT conduct electricity?

Q11. Dissolving concentrated acid in water is:

Q12. Why do all acids show similar chemical properties? What about bases?

Q13. Why does an aqueous solution of an acid conduct electricity while an alcohol or glucose solution does not?

Q14. Dry HCl gas does not change the colour of dry litmus paper. Why?

Q15. When an acid is being diluted, why must it go into the water rather than the water into it?

Q16. How is the concentration of hydronium ions affected when a solution of an acid is diluted?

Q17. Distinguish between a base and an alkali. Give one example of each kind.

Q18. Distinguish between strong and weak acids with two examples of each.

Q19. Lower pH means ______ hydrogen-ion concentration.

Q20. The approximate pH of gastric juice is:

Q21. Tooth decay starts when mouth pH falls below:

Q22. Rain is called acid rain when its pH is below:

Q23. What is the pH scale? How is the nature of a solution related to its pH value?

Q24. Why do living organisms need a narrow pH range? Give the consequence of rain becoming acidic.

Q25. What causes tooth decay? How does toothpaste help prevent it?

Q26. A patient suffers from acidity after overeating. Which type of substance gives relief, and how? Name one.

Q27. How is soil pH managed by farmers?

Q28. Two solutions A and B have pH 5 and pH 9. Which is acidic and which basic? Which will turn phenolphthalein pink?

Q29. Name the acid/base involved: (a) stomach digestion, (b) antacid, (c) bee sting, (d) treating acidic soil.

Q30. In the chlor-alkali process, chlorine is obtained at the:

Q31. Bleaching powder is used in drinking water to:

Q32. Blue copper sulphate crystals on heating turn:

Q33. Plaster of Paris is prepared by heating gypsum at:

Q34. Consider these statements about acids and bases. I. Acids taste sour and turn blue litmus red. II. Bases taste bitter and feel soapy. III. Bases turn red litmus blue. IV. Tasting a laboratory acid or base is a safe way to identify it. Which statements are correct?

Q35. A colourless solution turns red litmus blue, leaves phenolphthalein pink, and feels soapy between the fingers. The solution is:

Q36. Consider these indicator colours. I. Methyl orange is red in acid. II. Methyl orange is yellow in base. III. Phenolphthalein is colourless in acid. IV. Litmus is red in base. Which statements are correct?

Q37. Why are onion and vanilla called OLFACTORY indicators rather than ordinary ones?

Q38. Dilute sulphuric acid is poured on zinc granules and the gas given off is collected and brought near a burning splint. The expected result and its meaning are:

Q39. When CuO reacts with dilute HCl, the solution turns:

Q40. The reaction CuO + 2HCl → CuCl₂ + H₂O shows metal oxides are:

Q41. CO₂ reacting with Ca(OH)₂ shows non-metal oxides are:

Q42. When excess CO₂ passes through milky limewater, the milkiness:

Q43. Which metal will NOT release hydrogen from dilute HCl?

Q44. NaHCO₃ + HCl produces:

Q45. A bee sting (acidic) is best relieved by rubbing:

Q46. A nettle sting injects methanoic acid. It can be neutralised with:

Q47. Phenolphthalein is added to NaOH solution (pink). HCl is added till excess. The final colour is:

Q48. Which household substance would turn phenolphthalein pink?

Q49. Why does limewater turn milky with CO₂, and why does the milkiness disappear with excess CO₂? Give both equations.

Q50. What is observed when copper oxide is added to dilute hydrochloric acid? What does this show about metal oxides?

Q51. Why should curd and other sour substances not be kept in brass and copper vessels?

Q52. Do all bases react with all metals? Explain with an example.

Q53. Describe an activity to show the reaction of an acid with a metal — apparatus, procedure, observations, equation, gas test — and explain how the same setup with sodium carbonate would differ.

Q54. Explain neutralisation in detail: definition, an equation, the reaction type it belongs to, evidence that heat is evolved, and four applications in daily life.

Q55. On diluting an acid, the concentration of H₃O⁺ ions:

Q56. Alcohol contains hydrogen but is not an acid because it:

Q57. Distilled water barely conducts electricity because it:

Q58. HCl gas is dried in the litmus experiment by passing it through:

Q59. Which shows a WEAK acid's behaviour in water?

Q60. Dilute HCl vs concentrated acetic acid — the correct description is:

Q61. Which has MORE H₃O⁺ ions at equal concentration?

Q62. When NaOH pellets dissolve in water, the beaker:

Q63. The purpose of CONSTANT STIRRING while diluting acid is to:

Q64. Cu(OH)₂ is classified as:

Q65. A student adds sodium hydroxide pellets to water in a beaker and finds the beaker becomes hot. What does this show?

Q66. Which list contains ONLY strong acids?

Q67. What is the hydronium ion? Why is it formed?

Q68. Equal concentrations of HCl and acetic acid are given. Which will react faster with zinc, and why?

Q69. Four liquids give these pH values: gastric juice 1.2, tomato juice 4.1, milk 6.5, blood 7.4. Which is the MOST acidic?

Q70. Which is the MOST acidic?

Q71. pH 3 compared to pH 5 has H⁺ concentration:

Q72. Milk (pH 6.5) turning to curd will have its pH:

Q73. Which list is in INCREASING order of pH?

Q74. Fish die in acid-rain-affected lakes because:

Q75. Self-defence by pH: our skin surface is mildly acidic to:

Q76. Which change makes soil MORE acidic over time?

Q77. A gardener's hydrangeas bloom BLUE. The soil is likely:

Q78. Universal indicator is better than litmus for a science fair because it:

Q79. Explain why a bee sting and a nettle sting are relieved by the same kind of remedy.

Q80. What is meant by 'each pH unit is a ten-fold change'? Compare pH 4 with pH 6.

Q81. Explain the pH scale fully: what it measures, its range and zones, the ten-fold rule, how universal indicator reads it, and why pH — not just 'acid or base' — is the useful measure in real life. Include five substances with their pH values.

Q82. Why is the electrolysis of brine called the CHLOR-ALKALI process?

Q83. Consider these statements about baking soda. I. Its chemical name is sodium hydrogencarbonate. II. It is a mild, non-corrosive base. III. On heating it gives carbon dioxide. IV. It is a strong alkali like sodium hydroxide. Which statements are correct?

Q84. Heating baking soda gives:

Q85. The salt used to remove permanent hardness of water is:

Q86. The setting of plaster of Paris involves:

Q87. White anhydrous copper sulphate can be used to test for:

Q88. Which salt has NO water of crystallisation?

Q89. The number of water molecules in blue vitriol (CuSO₄·xH₂O) is:

Q90. In a soda-acid fire extinguisher, the reaction of NaHCO₃ with acid produces:

Q91. Which product of the chlor-alkali process goes into PVC?

Q92. Which pair is matched WRONGLY?

Q93. Which statement best explains why an indicator can tell an acid from a base at all?

Q94. Which of these best explains why a metal carbonate and a metal both react with an acid, yet give different gases?

Q95. Consider this test. I. A gas is passed into limewater and it turns milky. II. The milkiness is calcium carbonate. III. Passing more of the same gas clears the milkiness again. IV. The gas must be oxygen. Which statements are correct?

Q96. What is the best explanation of why an antacid must be a MILD base rather than a strong one?

Q97. Four everyday acids are found in vinegar, lemon, curd and a tamarind. In order, they are:

Q98. Milk of magnesia is a white suspension rather than a clear solution. Which statement explains this best?

Q99. Which of these reactions does NOT produce hydrogen gas?

Q100. Carbon dioxide is bubbled through limewater for a long time. The solution turns milky and then clear again. Which statement describes what happened?

Q101. Assertion (A): Zinc reacts with sodium hydroxide solution to give hydrogen gas. Reason (R): Every metal that releases hydrogen from an acid also releases it from an alkali.

Q102. Which is the correct explanation of why a metal oxide is described as basic and a non-metal oxide as acidic?

Q103. A soda-acid fire extinguisher works because the gas it produces does two useful things at once. They are:

Q104. 10 mL of NaOH is exactly neutralised by 8 mL of a given HCl. If 5 mL of the same NaOH is taken, the HCl needed is:

Q105. Which pair produces hydrogen gas?

Q106. Assertion: Curd should not be stored in copper or brass vessels. Reason: The lactic acid in curd reacts with the metal, forming harmful compounds.

Q107. Assertion: Metal oxides are called basic oxides. Reason: They react with acids to give salt and water.

Q108. A white powder fizzes with dilute HCl and the gas turns limewater milky. The powder could be:

Q109. A metal reacts with dilute H₂SO₄ giving a gas that pops. The products are:

Q110. Case: Two unlabeled bottles hold HCl and NaOH. One drop of phenolphthalein in samples of each shows:

Q111. Case: A student adds dilute HCl to (i) zinc and (ii) sodium carbonate. The gases evolved respectively are:

Q112. Fresh milk's pH is 6. On turning to curd, its pH will:

Q113. Which statement about neutralisation is INCORRECT?

Q114. Copper vessels used for lemon pickle get holes over years because:

Q115. A compound X of sodium reacts with dilute HCl to give brisk effervescence; the gas extinguishes a burning splint and turns limewater milky. Identify X (two possibilities) and write one equation.

Q116. With equations, show how (a) metal oxides behave like bases and (b) non-metal oxides behave like acids. Then explain why these two facts are described as 'mirror images' and give one everyday consequence of each.

Q117. An unknown white solid A fizzes with dilute HCl, releasing gas B that turns limewater milky; the milkiness clears on passing excess B, forming C. Solid A on strong heating gives solid D (used in white-washing after slaking) and the same gas B. Identify A, B, C, D with equations for every step.

Q118. Consider these statements about acids in water. I. All acids release hydrogen ions in water. II. The hydrogen ion attaches to water as the hydronium ion. III. Acid solutions conduct electricity because of these ions. IV. Any substance containing hydrogen is therefore an acid. Which statements are correct?

Q119. Which statement best explains why very different substances such as sodium hydroxide, calcium hydroxide and ammonia solution all behave alike?

Q120. Why is the hydrogen ion in an acid solution usually written as H₃O⁺ rather than simply H⁺?

Q121. Dry hydrogen chloride gas is passed over dry blue litmus paper and nothing happens; a drop of water is then added and the paper turns red. This shows that:

Q122. Assertion (A): Concentrated sulphuric acid must be added slowly to water, never water to the acid. Reason (R): The mixing releases a great deal of heat, and water poured onto the acid can boil at once and throw acid out of the vessel.

Q123. Consider these statements about alkalis. I. An alkali is a base that dissolves in water. II. All alkalis are bases. III. All bases are alkalis. IV. Copper hydroxide is a base but not an alkali. Which statements are correct?

Q124. Equal volumes of hydrochloric acid and acetic acid of the same concentration are put in two bulb circuits. Which observation is expected?

Q125. Which statement correctly distinguishes a STRONG acid from a CONCENTRATED one?

Q126. Four solutions of equal concentration are tested. Which contains the FEWEST ions?

Q127. Which statement best explains what actually happens when any acid neutralises any base in water?

Q128. Assertion (A): A solution of glucose conducts electricity, since the molecule contains hydrogen. Reason (R): Conduction in a solution needs free ions, and glucose dissolves as whole molecules without releasing any.

Q129. Assertion (A): Moist ammonia gas turns red litmus blue, but dry ammonia gas does not. Reason (R): Ammonia releases hydrogen ions once water is present, and those ions change the colour.

Q130. Two colourless solutions are tested: X conducts electricity strongly and turns blue litmus red; Y conducts hardly at all and has no effect on litmus. X and Y could be:

Q131. Consider these classifications. I. Sodium hydroxide is a strong base and an alkali. II. Ammonium hydroxide is a weak base and an alkali. III. Calcium hydroxide is a base that dissolves only slightly. IV. Copper hydroxide is an alkali. Which statements are correct?

Q132. Assertion: Dry HCl gas does not change dry litmus. Reason: HCl produces H⁺ ions only in the presence of water.

Q133. Assertion: Glucose solution does not conduct electricity. Reason: Glucose contains no hydrogen atoms.

Q134. Two solutions of equal concentration: HCl and acetic acid. The one reacting FASTER with zinc granules is:

Q135. A teacher dilutes H₂SO₄ by the correct method. The correct order is:

Q136. If 10 mL of concentrated HCl is diluted to 1 L, the number of H₃O⁺ ions:

Q137. Case: A student's 'acid' sample doesn't light the conductivity bulb and doesn't fizz with zinc. The sample is most likely:

Q138. Case: Ammonia gas from a bottle turns moist red litmus blue but leaves dry red litmus unchanged. This parallels the dry-HCl experiment because:

Q139. Which statement about a weak acid is TRUE?

Q140. The ion responsible for turning phenolphthalein pink is effectively:

Q141. During neutralisation, the spectator ions (like Na⁺ and Cl⁻):

Q142. Why is the SAME volume of water safer than the same volume of acid as the 'receiving' liquid during dilution?

Q143. Why does distilled water not conduct electricity, whereas rainwater does?

Q144. Describe the conductivity experiment comparing dilute HCl, dilute H₂SO₄, glucose and alcohol solutions — setup, observations, and the two conclusions it establishes about the nature of acids.

Q145. Describe the dry-HCl experiment in detail (with the role of the guard tube) and explain what it proves about the role of water in acidity. Extend the same logic to ammonia and bases.

Q146. Explain everything that happens — chemically and thermally — when concentrated sulphuric acid is diluted, why the order of mixing matters for safety, and what dilution does to the acidity of the solution.

Q147. Classify the following and justify each: NaOH, Cu(OH)₂, HCl, acetic acid, NH₄OH, Ca(OH)₂ — into (a) strong/weak, (b) acid/base, (c) alkali or not (for the bases). Then explain why the strong/weak distinction matters practically, with one example.

Q148. Consider these statements about the pH scale. I. pH below 7 is acidic and above 7 is basic. II. Each step down the scale means ten times more hydrogen ions. III. Pure water has pH 7. IV. A pH of 15 is common in strong alkalis. Which statements are correct?

Q149. Solution X has pH 2 and solution Y has pH 5. The hydrogen-ion concentration in X compared with Y is:

Q150. Which of these best explains why pH is written as a scale of numbers rather than simply as a concentration?

Q151. Why is universal indicator more useful than litmus for examining a soil sample?

Q152. Consider these statements about acid rain. I. Rain is called acid rain when its pH falls below 5.6. II. Oxides of sulphur and nitrogen dissolve in rain to cause it. III. It lowers the pH of rivers and harms aquatic life. IV. Ordinary rain is exactly neutral at pH 7. Which statements are correct?

Q153. Human blood is held at a pH of about 7.4 and a shift to 7.0 would be life-threatening. This shows that:

Q154. What is the best explanation of why brushing after eating sweets protects the teeth?

Q155. Assertion (A): A bee sting is rubbed with baking soda while a wasp sting is not. Reason (R): A bee sting injects an alkali, which a mild base neutralises, whereas a wasp sting is acidic.

Q156. Four remedies are offered for four problems. Which pairing uses the WRONG chemistry?

Q157. Consider these statements about pH in everyday life. I. Excess stomach acid is treated with a mild base. II. Tooth decay begins below a mouth pH of 5.5. III. Plants grow well only in a particular range of soil pH. IV. A farmer adds lime to soil that is too basic. Which statements are correct?

Q158. A gardener finds that the same hydrangea plant bears blue flowers in one bed and pink in another. The best explanation is that:

Q159. Which is the correct explanation of why acid rain kills fish in a lake even though the fish never leave the water?

Q160. Which statement best explains why the stomach makes hydrochloric acid at a pH near 1.2 without digesting itself?

Q161. Fresh milk has a pH of about 6. A milkman adds a little baking soda before selling it. Which statement is correct?

Q162. Fresh milk's pH is 6. A milkman adds a little baking soda. The pH:

Q163. Why does milk with added baking soda take LONGER to set as curd?

Q164. Two solutions: X turns universal indicator orange, Y turns it violet. Then:

Q165. Assertion: A solution of pH 2 is 100 times more acidic than one of pH 4. Reason: Each pH unit represents a ten-fold change in H⁺ concentration.

Q166. Assertion: Tooth enamel is safe from bases but attacked by acids. Reason: Calcium phosphate does not dissolve in bases but corrodes below pH 5.5.

Q167. A very dilute HCl solution could have pH close to:

Q168. Case: A lake's pH dropped from 6.8 to 5.2 over a decade near an industrial area. The most likely cause and consequence are:

Q169. Case: A child who sips fizzy drinks all day (pH ~2.5) and never rinses is most at risk of:

Q170. Which pairing of problem → remedy uses the WRONG chemistry?

Q171. Blood pH shifting from 7.4 to 7.0 would be:

Q172. Rainwater collected in a clean area shows pH 6.0. This indicates:

Q173. The pH inside our small intestine is basic. The organ chiefly responsible for neutralising the acidic food mass is the:

Q174. Fresh milk has pH 6. Why does a milkman shift it slightly towards alkaline by adding baking soda, and why does such milk take longer to set as curd?

Q175. 'pH quietly manages our health from mouth to stomach.' Justify this statement by explaining tooth decay, gastric acidity and their remedies as pH phenomena, including all relevant substances and numbers.

Q176. Describe how pH problems arise and are corrected in agriculture and in the environment: soil pH management and acid rain — causes, consequences, and remedies, with the relevant chemistry.

Q177. Design a simple experiment using pH paper (or universal indicator) to arrange five unlabeled kitchen liquids — lemon juice, soap solution, milk, vinegar and baking-soda solution — in order of acidity, predicting the expected colours and final ranking, and adding one confirmation test for the most acidic sample.

Q178. Consider these statements about the pH of salt solutions. I. A salt of a strong acid and a strong base is neutral. II. A salt of a strong acid and a weak base is acidic. III. A salt of a weak acid and a strong base is basic. IV. Every salt solution is neutral, since the acid and base cancelled out. Which statements are correct?

Q179. Three salt solutions are tested with universal indicator: sodium chloride gives green, ammonium chloride orange, and sodium carbonate blue. The best explanation is that:

Q180. Assertion (A): A solution of washing soda feels soapy and turns red litmus blue. Reason (R): Washing soda is sodium carbonate decahydrate, with ten molecules of water of crystallisation.

Q181. In the electrolysis of brine, three products form at three places. Chlorine, hydrogen and sodium hydroxide appear respectively at:

Q182. Which of these best explains why bleaching powder is used both to whiten cloth and to treat drinking water?

Q183. Bleaching powder is made by passing chlorine over dry slaked lime. Which statement about this is correct?

Q184. What is the best explanation of why the formula of washing soda is written Na₂CO₃·10H₂O rather than simply Na₂CO₃?

Q185. Blue copper sulphate crystals are heated in a test tube, turn white, and droplets collect at the cooler mouth of the tube. Adding water to the white solid restores the blue. This shows that:

Q186. Assertion (A): Plaster of Paris may safely be stored in an open container in a damp room. Reason (R): It takes up water from the air and sets into hard gypsum, after which it is useless as a plaster.

Q187. Gypsum is heated to make plaster of Paris. Which statement describes the change correctly?

Q188. Which is the correct explanation of why baking POWDER contains a mild edible acid as well as baking soda?

Q189. Consider these statements about heating baking soda. I. It gives sodium carbonate, water and carbon dioxide. II. The carbon dioxide makes bread and cake rise. III. The reaction is a thermal decomposition. IV. The sodium carbonate left behind tastes bitter. Which statements are correct?

Q190. Which sequence correctly makes washing soda starting from common salt?

Q191. A doctor applies a wet plaster of Paris bandage to a fracture and the cast becomes warm as it hardens. This shows that:

Q192. The three products of the chlor-alkali process go to three different industries. Sodium hydroxide, chlorine and hydrogen are used respectively in:

Q193. Assertion: Plaster of Paris must be stored in airtight containers. Reason: Moisture converts it slowly into gypsum, which cannot set again.

Q194. Assertion: A solution of sodium acetate (CH₃COONa) is basic. Reason: It is the salt of a weak acid and a strong base.

Q195. 10 g of blue CuSO₄·5H₂O heated to constant mass weighs noticeably less because:

Q196. A doctor's fracture cast becomes warm while hardening. This shows the setting of PoP is:

Q197. Case: A factory needs to bleach wood pulp AND disinfect its water supply with ONE chemical. It should buy:

Q198. Case: A sculptor's plaster bag, left open through monsoon, has turned into hard lumps. The chemistry is:

Q199. Which sequence correctly makes washing soda starting from brine?

Q200. The chlor-alkali process is economically powerful because: