Material Around Us Part 3: MCQs (Q51–Q75)
Part 3 — Questions 51–75 (Physical & chemical changes, reversible & irreversible changes)
51. Which of the following is a physical change?
A. Rusting of iron
B. Melting of ice to water ← Correct answer: B
C. Burning of paper
D. Baking a cake
Explanations:
A/C/D) Chemical changes (new substances formed).
B) Correct — melting is a change of state; reversible physical change.
52. Which of the following is an irreversible change?
A. Dissolving sugar in water (can be recovered)
B. Burning of wood to ash ← Correct answer: B
C. Water freezing to ice (reversible)
D. Stretching a rubber band within elastic limit (reversible)
Explanations:
A/C/D) Reversible physical changes.
B) Correct — combustion produces new substances; cannot recover original wood.
53. Rusting of iron is an example of
A. Physical change only
B. Chemical change (iron reacts with oxygen to form iron oxide) ← Correct answer: B
C. Change of state
D. Melting
Explanations:
A/C/D) Incorrect.
B) Correct — rust is a new compound formed by chemical reaction.
54. Which sign indicates a chemical change has occurred?
A. Change in shape only
B. Evolution of gas, permanent colour change, formation of precipitate, temperature change ← Correct answer: B
C. Everything is reversible always
D. Only expansion on heating
Explanations:
A/C/D) Not specific.
B) Correct — chemical changes often show such signs.
55. When milk turns sour (curdles), this is due to
A. Melting of milk solids
B. Chemical change by action of bacteria producing lactic acid ← Correct answer: B
C. Freezing only
D. Magnetism
Explanations:
A/C/D) Incorrect.
B) Correct — souring involves chemical change and formation of curd.
56. Which of the following is a reversible physical change?
A. Burning of coal
B. Melting and re-solidifying of wax (if no chemical reaction) ← Correct answer: B
C. Rusting of metal
D. Cooking an egg
Explanations:
A/C/D) Irreversible chemical changes.
B) Correct — physical state change reversible.
57. Which reaction is an example of chemical change with evolution of gas?
A. Ice melting
B. Vinegar reacting with baking soda producing CO₂ gas ← Correct answer: B
C. Dissolving sugar in water
D. Stretching a spring
Explanations:
A/C/D) Physical changes.
B) Correct — reaction produces carbon dioxide gas bubbles.
58. Which is NOT a chemical change?
A. Burning a paper
B. Mixing water and sugar (dissolving) ← Correct answer: B
C. Cooked food formation
D. Tarnishing of silver
Explanations:
A/C/D) Chemical changes producing new substances.
B) Correct — dissolving is a physical change (sugar can be recovered).
59. Which process is used to recover dissolved salt from seawater (physical process)?
A. Burning the sea
B. Evaporation and crystallisation ← Correct answer: B
C. Rusting iron in sea
D. Adding acid to seawater
Explanations:
A/C/D) Nonsense/incorrect.
B) Correct — physical separation by removing water.
60. Which of the following is an example of a chemical change in kitchen?
A. Freezing juice to make ice pops
B. Baking cake (ingredients react to form new substance) ← Correct answer: B
C. Boiling water only (physical change)
D. Cutting vegetables (physical)
Explanations:
A/C/D) Physical processes.
B) Correct — baking causes new compounds to form (irreversible change).
61. Photosynthesis in plants is a chemical change because
A. Light disappears only
B. Carbon dioxide and water form glucose and oxygen (new substances) ← Correct answer: B
C. Leaves change colour only physically
D. Roots grow only
Explanations:
A/C/D) Incomplete descriptions.
B) Correct — photosynthesis synthesises new chemical compounds.
62. Which is a sign that a physical change has occurred?
A. Colour change that is permanent only
B. Change of state or shape without new substance formation ← Correct answer: B
C. Production of new gas always
D. Creation of heat by chemical reaction only
Explanations:
A/C/D) Could be chemical indicators.
B) Correct — physical changes involve forms, not composition.
63. Which of the following changes is caused by mixing an acid with a base (neutralisation)?
A. Only change in temperature always physical
B. Chemical change producing salt and water (and sometimes gas) ← Correct answer: B
C. No reaction at all ever
D. Physical mixing only
Explanations:
A/C/D) Wrong.
B) Correct — neutralisation is chemical.
64. Burning of a candle involves which of the following?
A. Only melting of wax (physical)
B. Both melting of wax (physical) and combustion of wax vapour (chemical) ← Correct answer: B
C. Only a magnetic reaction
D. No change at all
Explanations:
A) Partial — burning also chemical.
B) Correct — wax melts and vapour burns producing new substances (CO₂, H₂O).
C/D) Incorrect.
65. Which of these is a chemical change that is useful for making curd from milk?
A. Heating milk only (sterilisation)
B. Adding curd/acid or bacterial culture to milk (biochemical change) ← Correct answer: B
C. Freezing milk into ice cream only
D. Mixing milk with sugar only
Explanations:
A/C/D) Not the main curdling mechanism.
B) Correct — bacteria convert lactose to lactic acid causing protein coagulation (curd).
66. Which of the following changes is reversible?
A. Burning matchstick
B. Dissolving salt in water (salt can be recovered by evaporation) ← Correct answer: B
C. Rusting of nail
D. Cooking an egg
Explanations:
A/C/D) Irreversible chemical changes.
B) Correct — physical change reversible by removing solvent.
67. Which of the following indicates a physical change?
A. Formation of a precipitate from two solutions (chemical)
B. Change in shape of clay by rolling into a ball (physical) ← Correct answer: B
C. Burning of paper (chemical)
D. Milk turning to curd (chemical)
Explanations:
A/C/D) Chemical processes.
B) Correct — only physical rearrangement of the material.
68. Which example is a chemical change accompanied by release of heat (exothermic)?
A. Melting ice
B. Burning wood ← Correct answer: B
C. Dissolving salt in water (usually mild endothermic)
D. Freezing water
Explanations:
A/C/D) Physical or endothermic.
B) Correct — combustion releases heat.
69. Which of the following is a result of mixing baking soda and vinegar?
A. Colourless liquid with no change
B. Frothing due to CO₂ gas evolution — chemical reaction ← Correct answer: B
C. Only a physical separation of solids
D. Making metallic bonds stronger
Explanations:
A/C/D) Incorrect.
B) Correct — reaction forms carbon dioxide gas bubbles.
70. Which is true about dissolving?
A. Dissolving always involves chemical bond formation
B. Dissolving is a physical change for most solids in liquids (no new substance) ← Correct answer: B
C. Dissolving always irreversible
D. Dissolving turns solids into gases directly always
Explanations:
A/C/D) Incorrect generalizations.
B) Correct — solute molecules disperse in solvent (often reversible).
71. Which of the following would be considered a chemical change in food?
A. Freezing vegetables (no chemical)
B. Fermentation of milk to make yogurt ← Correct answer: B
C. Cutting bread into slices
D. Peeling fruit
Explanations:
A/C/D) Physical changes.
B) Correct — biochemical/chemical change producing new compounds.
72. Which process could separate a homogeneous solution into its components without chemical change?
A. Filtration
B. Distillation (evaporating and condensing solvent) ← Correct answer: B
C. Burning mixture
D. Mixing with acid only
Explanations:
A) Filtration removes insoluble particles only.
B) Correct — distillation recovers solvents and solutes physically.
C/D) Cause chemical transformations or irrelevant.
73. Which of these is a sign of a chemical change in an experiment?
A. Temporary change in shape only
B. Formation of gas, precipitate, permanent colour change, temperature change ← Correct answer: B
C. Only physical mixing with no new substance
D. Change that is purely reversible by heating
Explanations:
A/C/D) Not reliable chemical indicators.
B) Correct — these are classic signs.
74. Which is an example where both physical and chemical changes occur?
A. Dissolving rock salt in water only (physical)
B. Cooking sugar to make caramel (melting + chemical decomposition and browning reactions) ← Correct answer: B
C. Cutting vegetables (physical)
D. Melting lead (physical)
Explanations:
A/C/D) Mostly physical.
B) Correct — heating sugar causes melting and chemical changes (caramelization).
75. Which illustrates a reversible physical change used in everyday life?
A. Burning paper to ashes
B. Freezing and melting of water (ice ↔ water) ← Correct answer: B
C. Rusting of a bicycle chain
D. Browning of apple when cut (chemical)
Explanations:
A/C/D) Irreversible or chemical.
B) Correct — phase changes reversible with temperature.