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When candle burns:

a. its size decreases.

b. there is melting of wax.

c. flame and soot can be seen.

d. melted wax also solidies.

From the observations, which one of the following is correct?


1. a is a physical change and others are chemical changes.
2. c is a chemical change and others are physical changes.
3. a & b are physical changes and c & d are chemical changes.
4. a, b and c are physical changes.

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Correct Answer - Option 2 : c is a chemical change and others are physical changes.

Concept:

Physical Change  Chemical Change 
  • A temporary change.
  • A permanent change.
  • Affects only the physical properties that are size, shape, etc. 
  • It affects both physical and chemical properties as well as the composition
  • Despite the fact that a substance's molecules are rearranged when it experiences a physical change, its composition remains the same.
  • A substance's molecular composition is completely altered when it experiences a chemical transformation. As a result, chemical transformations result in the production of new substances.
  • No new substance is formed. 
  • A new substance is formed.
  • The physical change is reversible, meaning the original material can be regained.
  • Chemical transformations are irreversible, which means that the original substance cannot be restored.

Examples - 

Melting of ice, Melting of wax, Boiling of water, etc. 

Examples - 

Burning of candle, Burning of paper, burning of wood, etc. 

Explanation:

  • The given changes are - 
    • a. its size decreases - Physical Change
    • b. there is melting of the wax - Physical Change 
    • c. flame and soot can be seen - Chemical Change 
    • d. melted wax also solidifies - Physical change 
  • a, b and d are physical changes because no new substances are formed and there is no change in the chemical composition of the wax. ( Only physical properties are changed.)
  • In c, a new substance can be seen which is the flame and there is a change in the chemical composition as well as the chemical properties. 
  • The correct answer to this question is - c is a chemical change and the rest are physical changes. 

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