Chemical Reactions and Equations · Class 10 Science: 162 MCQs with answers

Q1. Which of these is a chemical change?

Q2. In a chemical equation, the substances on the LEFT of the arrow are the:

Q3. Balancing of equations is based on the law of conservation of:

Q4. An equation with correct formulas but unequal atoms is called a:

Q5. While balancing, we are allowed to change only the:

Q6. Magnesium burns in air with a:

Q7. The product of burning magnesium is:

Q8. An insoluble solid formed during a reaction in solution is called a:

Q9. Which is a sign that a chemical reaction has occurred?

Q10. What makes a chemical equation balanced, and what goes wrong if it is not?

Q11. Why is a magnesium ribbon cleaned before it is burnt in air?

Q12. List any four observations that help us determine whether a chemical reaction has taken place.

Q13. What information do the symbols (s), (l), (g), (aq), ↑ and ↓ convey in an equation?

Q14. Distinguish between a physical change and a chemical change with one example each.

Q15. CaO + H₂O → Ca(OH)₂ is a:

Q16. Heating calcium carbonate gives:

Q17. The decomposition of AgCl by light is used in:

Q18. In water electrolysis, the volume of hydrogen compared to oxygen is:

Q19. An iron nail dipped in copper sulphate solution becomes:

Q20. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl is a:

Q21. Reactions that release heat are called:

Q22. What is a combination reaction? Write the reaction of quicklime with water and one use of the product.

Q23. Why is the reaction between quicklime and water called both a combination and an exothermic reaction?

Q24. Why is silver chloride kept in dark-coloured bottles? Write the relevant equation.

Q25. What is observed when an iron nail is dipped in copper sulphate solution? Name the reaction type and write the equation.

Q26. What is a precipitation reaction? Explain with an example.

Q27. When copper powder is heated in air, its surface turns:

Q28. The slow eating away of metals by their surroundings is:

Q29. The black coating on tarnished silver is:

Q30. The oxidation of fats and oils in food is called:

Q31. Substances that prevent oxidation of food are called:

Q32. Define oxidation and reduction with one example each.

Q33. What is corrosion? Give the corrosion products of iron, silver and copper.

Q34. State four methods of preventing rusting of iron.

Q35. What is rancidity? Why do fried food items develop an unpleasant smell over time?

Q36. Explain why food items containing fats and oils are packed in nitrogen-flushed packets.

Q37. Consider these statements about a balanced chemical equation. I. It shows which substances react and which are formed. II. It shows the relative numbers of particles taking part. III. It shows how fast the reaction happens. IV. It obeys the law of conservation of mass. Which statements are correct?

Q38. Consider these state symbols. I. (s) means a solid. II. (aq) means dissolved in water. III. (l) means a pure liquid. IV. (aq) and (l) mean the same thing. Which statements are correct?

Q39. The correctly balanced form of H₂ + O₂ → H₂O is:

Q40. Writing H₂O₂ instead of 2H₂O to balance is wrong because:

Q41. The balanced equation for iron reacting with steam is:

Q42. In CH₄ + 2O₂ → CO₂ + 2H₂O, the count of oxygen atoms on each side is:

Q43. Which equation is balanced?

Q44. The correct state symbols for common salt solution reacting are shown by:

Q45. In the equation CaCO₃(s) --Δ--> CaO(s) + CO₂(g), the Δ indicates:

Q46. Hydrogenation of vegetable oil uses which catalyst on the arrow?

Q47. A white magnesium oxide ash weighs MORE than the magnesium ribbon burnt. This is because:

Q48. The total mass of a sealed flask containing reacting chemicals will, after the reaction:

Q49. Balance the equation: Fe + H₂O → Fe₃O₄ + H₂, and add state symbols given the water is steam.

Q50. 2 g of hydrogen reacts completely with 16 g of oxygen. What mass of water is formed, and which law lets you answer without experiment?

Q51. Why is respiration considered a chemical reaction? Write its word equation.

Q52. Balance: (a) NaOH + H₂SO₄ → Na₂SO₄ + H₂O, (b) BaCl₂ + Na₂SO₄ → BaSO₄ + NaCl.

Q53. Explain the complete procedure for balancing a chemical equation by the hit-and-trial method, using Fe + H₂O → Fe₃O₄ + H₂ as your worked example. Include the underlying law and the rules that must never be broken.

Q54. Describe the activity of burning magnesium ribbon in air: procedure, precautions, observations, the balanced equation with states, and the explanation of why this is a chemical change. Also explain why the product weighs more than the ribbon.

Q55. Assertion (A): The reaction between quicklime and water is a combination reaction as well as an exothermic one. Reason (R): Two substances join to give a single product, and heat is given out in the process.

Q56. Which of these reactions ABSORBS energy from its surroundings rather than releasing it?

Q57. On heating green ferrous sulphate crystals, the residue is:

Q58. Heating lead nitrate produces brown fumes of:

Q59. White-washed walls turn shiny because Ca(OH)₂ reacts with:

Q60. Barium sulphate's colour and solubility are:

Q61. Which pair shows a combination AND an exothermic reaction together?

Q62. Describe what is observed when ferrous sulphate crystals are heated, with the balanced equation and the type of reaction.

Q63. In the electrolysis of water, why is the gas collected in one test tube double the volume of the other? Name both gases.

Q64. Distinguish between displacement and double displacement reactions with one example of each.

Q65. Classify each as exothermic or endothermic: (a) burning of natural gas, (b) decomposition of calcium carbonate, (c) respiration, (d) photosynthesis.

Q66. Dip an iron nail into copper sulphate solution and the blue fades. What is happening to cause that?

Q67. Explain the four types of chemical reactions with one balanced equation and one observable feature each, and show how the 'Join, Split, Kick, Swap' pattern helps classify any given reaction.

Q68. In CuO + H₂ → Cu + H₂O, the OXIDISING agent is:

Q69. In ZnO + C → Zn + CO, carbon acts as the:

Q70. Which nail will NOT rust?

Q71. Which is NOT a method of preventing corrosion?

Q72. Stainless steel resists rusting because it is:

Q73. Food kept in a refrigerator turns rancid more slowly because:

Q74. Which food is most prone to rancidity?

Q75. Which statement correctly distinguishes corrosion from rancidity?

Q76. The best ONE-WORD common cause behind rusting gates, black silver, green copper and stale chips is:

Q77. Why is CuO + H₂ → Cu + H₂O called a redox reaction? Identify all four roles.

Q78. What happens when copper powder is heated in a china dish? How can the change be reversed? Give both equations.

Q79. Describe the experiment showing that rusting needs both air and moisture.

Q80. In the reaction ZnO + C → Zn + CO, identify the substance oxidised, the substance reduced, and both agents.

Q81. Why is corrosion a serious economic problem? Give two examples of things damaged by it.

Q82. Why are conditions such as heat, light or a catalyst written ABOVE the arrow rather than beside the reactants?

Q83. Balance: Fe₂O₃ + C → Fe + CO₂. The coefficients of Fe₂O₃, C, Fe and CO₂ in order are:

Q84. Assertion (A): To balance an equation we may change the coefficient in front of a formula but never a subscript inside it. Reason (R): Changing a subscript changes the substance itself, while changing a coefficient only changes how many units of it there are.

Q85. Which statement best explains why the melting of wax is a physical change but the burning of wax is a chemical one?

Q86. Balance: Al + O₂ → Al₂O₃. The coefficients (Al, O₂, Al₂O₃) are:

Q87. Balance: Na + H₂O → NaOH + H₂. The coefficients are:

Q88. Balance: HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O. The coefficients are:

Q89. Two clear colourless solutions are mixed and a white solid at once settles out, though nothing is heated and no gas escapes. Which conclusion is justified?

Q90. Assertion: Equations are balanced to obey the law of conservation of mass. Reason: Atoms are only rearranged in chemical reactions, never created or destroyed.

Q91. Assertion: 2H₂O and H₂O₂ represent the same thing in an equation. Reason: Both contain hydrogen and oxygen.

Q92. 10 g of CaCO₃ on complete decomposition gave 5.6 g of CaO. The mass of CO₂ released is:

Q93. In a reaction, 4 g of hydrogen combines with 32 g of oxygen. The mass of water formed is:

Q94. The number of atoms in total on the LEFT of 2H₂ + O₂ → 2H₂O is:

Q95. Case: A student heats a blue-green solid; a gas turns limewater milky and a black residue remains. She has evidence of a reaction from:

Q96. Case: Vinegar poured on baking soda in a sealed flask on a balance shows no change in reading despite vigorous fizzing. This demonstrates:

Q97. Vinegar is poured on baking soda in an OPEN flask standing on a balance. The reading falls steadily as the fizzing goes on. The reason is that:

Q98. Which of these equations is already balanced as written?

Q99. 56 g of iron reacts completely with 32 g of sulphur to form iron sulphide. No gas escapes. The mass of iron sulphide formed is:

Q100. Consider these statements about the equation 2Mg + O₂ → 2MgO. I. Two atoms of magnesium combine with one molecule of oxygen. II. The mass of the ash is greater than the mass of the ribbon burnt. III. Oxygen is taken from the air, so the air around loses mass. IV. Magnesium is decomposed into simpler substances. Which statements are correct?

Q101. Write balanced equations: (a) hydrogen + chlorine → hydrogen chloride, (b) barium chloride + aluminium sulphate → barium sulphate + aluminium chloride.

Q102. A student writes these unbalanced equations: (a) HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + H₂O, (b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O, (c) NaCl + AgNO₃ → AgCl + NaNO₃, (d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl. Balance all four, add ↓ where precipitates form, and state which of the five 'signs of reaction' each of (c) and (d) would show.

Q103. Design a simple experiment to VERIFY the law of conservation of mass using barium chloride and sodium sulphate solutions. Give the apparatus, procedure, observations, calculation logic and conclusion — and explain why the experiment fails if performed in an open beaker with a gas-forming reaction instead.

Q104. Consider these statements about combination reactions. I. Two or more substances join to form a single product. II. They are very often exothermic. III. The reactants may be elements or compounds. IV. The product always contains more atoms than either reactant. Which statements are correct?

Q105. Which of these best explains why decomposition is called the opposite of combination?

Q106. A student adds water to a white solid in a beaker. The mixture hisses, the beaker becomes hot to touch, and a white suspension forms. The solid is most likely:

Q107. Consider these statements about the decomposition of silver chloride in sunlight. I. White silver chloride turns grey. II. The grey colour is silver metal set free. III. Chlorine gas is released. IV. The energy needed is supplied by heat, not light. Which statements are correct?

Q108. In the electrolysis of water, 20 mL of gas collects over one electrode while the other collects 10 mL in the same time. The 20 mL of gas is:

Q109. An iron nail is left in blue copper sulphate solution. Which statement best explains the two changes seen?

Q110. Which of these displacement reactions will NOT take place?

Q111. Consider these statements about double displacement reactions. I. Two compounds exchange their ions. II. One product is often an insoluble precipitate. III. Neutralisation of an acid by a base is one kind of it. IV. A free element is always among the products. Which statements are correct?

Q112. Assertion (A): Respiration is an endothermic reaction, since no flame is seen. Reason (R): Glucose is oxidised in the cells and the energy released keeps the body warm and drives its activities.

Q113. Green crystals of ferrous sulphate are heated strongly in a dry test tube. Which set of observations is correct?

Q114. Four metals are placed each in a solution of the others' salts. Which metal displaces the greatest number of the other three?

Q115. Heating 20 g of calcium carbonate drove off 8.8 g of carbon dioxide. The mass of quicklime left behind is:

Q116. Why is neutralisation counted as a double displacement reaction?

Q117. Freshly white-washed walls take two or three days to develop their shine. Which statement explains this best?

Q118. Consider these statements about the energy of reactions. I. Most decomposition reactions are endothermic. II. Most combination reactions are exothermic. III. The decomposition of limestone needs continuous heating. IV. A reaction that gives out heat must also give out light. Which statements are correct?

Q119. Three decompositions are driven by three different forms of energy: limestone by X, silver bromide by Y, and water by Z. X, Y and Z are:

Q120. A piece of zinc is dropped into dilute hydrochloric acid and a gas bubbles off briskly. Which statement about this reaction is correct?

Q121. Which observation belongs to heating copper sulphate crystals (blue vitriol)?

Q122. Assertion: Iron displaces copper from CuSO₄ solution. Reason: Iron is more reactive than copper.

Q123. Assertion: Silver chloride is stored in dark-coloured bottles. Reason: AgCl decomposes to silver and chlorine in sunlight.

Q124. The reaction C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy occurs in:

Q125. Case: Solutions of lead nitrate and potassium iodide are mixed; a yellow solid appears. This is:

Q126. Case: A test tube gets noticeably COLD as a salt dissolves and reacts. The process is:

Q127. Marble chips react with dilute HCl giving brisk effervescence. The gas and its test are:

Q128. Which correctly matches reaction to type?

Q129. A double displacement reaction is confirmed most directly by observing:

Q130. Describe the electrolysis-of-water activity in detail: apparatus, why acid is added, observations at each electrode, the balanced equation, the type of reaction, and how you would test the two gases collected.

Q131. A shiny iron nail is placed in copper sulphate solution while an identical nail is kept aside for comparison. Describe the experiment's setup, observations after 20 minutes, the balanced equation, the conclusion about reactivity, and TWO further predictions this conclusion lets you make (with equations).

Q132. Write the story of white-washing a wall as a chain of three chemical reactions (preparation of slaked lime, application, and the shine developing), classifying each reaction by type and energy change, with balanced equations.

Q133. Consider these statements about oxidation and reduction. I. Gain of oxygen is oxidation. II. Loss of hydrogen is oxidation. III. Gain of hydrogen is reduction. IV. Oxidation can happen on its own, without anything being reduced. Which statements are correct?

Q134. What is the best explanation of why oxidation and reduction are said to be two halves of one reaction?

Q135. Assertion (A): In the reaction ZnO + C → Zn + CO, carbon is the reducing agent. Reason (R): Zinc oxide is a white solid that turns yellow on heating.

Q136. Black copper oxide is heated in a stream of hydrogen gas and turns brown. Which statement correctly describes what has happened?

Q137. In the reaction CuO + H₂ → Cu + H₂O, the substance OXIDISED is:

Q138. Consider these statements about the rusting of iron. I. Rust is hydrated iron(III) oxide. II. Both air and moisture are needed for rusting. III. Rust flakes off, exposing fresh iron underneath. IV. Rust forms a tight protective layer that stops further attack. Which statements are correct?

Q139. Three metals corrode in three different ways: iron turns reddish-brown, silver turns black, and copper turns green. The three products are respectively:

Q140. Why are packets of chips filled with nitrogen rather than simply sealed with the air inside?

Q141. Which is the correct explanation of why painting, oiling and galvanising all protect iron from rusting?

Q142. Three iron nails are kept for a week — one in boiled water under a layer of oil, one in dry air over anhydrous calcium chloride, and one in ordinary water open to the air. Rust appears on:

Q143. Consider these statements about oxidising and reducing agents. I. The oxidising agent supplies oxygen to the other substance. II. The reducing agent removes oxygen from the other substance. III. The oxidising agent is itself reduced. IV. The reducing agent is itself reduced as well. Which statements are correct?

Q144. Which statement explains why a substance can be an oxidising agent in one reaction and not in another?

Q145. Iron railings by the sea rust much faster than the same railings inland. The best reason is that sea air:

Q146. A shiny copper wire is heated strongly in air and turns black; the black wire is then heated in hydrogen and turns shiny brown again. This pair of changes shows:

Q147. In the reaction MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂, HCl is:

Q148. In the reaction MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂, manganese dioxide acts as the:

Q149. Assertion: In CuO + H₂, copper oxide is the oxidising agent. Reason: It provides the oxygen that oxidises the hydrogen.

Q150. Assertion: Galvanised iron resists rust even when the zinc coat is scratched. Reason: Zinc, being more reactive, corrodes in preference to the iron.

Q151. Ships' hulls corrode faster than village gates because:

Q152. Oil and fat containing food items are flushed with nitrogen, NOT carbon dioxide, mainly because nitrogen is:

Q153. Case: A silver bowl blackens fastest in a home where eggs are often boiled. The connection is:

Q154. Case: Butter kept uncovered in summer smells 'off' within days, but a sealed frozen pack lasts months. The TWO defences at work in the pack are:

Q155. Which equation represents reduction of the underlined-style substance (Fe₂O₃)?

Q156. In that thermite-style reaction, aluminium acts as:

Q157. The copper-cycle demo shows oxidation and reduction:

Q158. Why does cut apple turn brown? (Extension of this topic's idea)

Q159. Explain oxidation, reduction and redox reactions using the copper cycle experiment (both legs) and the ZnO + C reaction, identifying agents in each case, and state the general rule connecting 'substance oxidised' with 'reducing agent'.

Q160. Describe the three-test-tube rusting experiment in full detail — setup, controls, observations, conclusion — and use its conclusion to explain WHY each of the four common rust-prevention methods works.

Q161. Compare corrosion and rancidity as 'two faces of oxidation': define both, give their victims, visible signs, chemical products, damages caused, and prevention methods — ending with the single principle behind all the preventions.

Q162. A shopkeeper stores silver jewellery, iron tools and packets of fried snacks. Over months, the silver blackens, the tools rust, and unsold open snacks smell bad — while nitrogen-sealed packets stay fresh. Explain the chemistry behind all four observations and advise the shopkeeper on protecting each item.