Question

Q. With reference to physical and chemical change consider the following statements:

Which of the above given statements is/are correct?

• A.
  1 and 2 only
• B.
  1 and 3 only
• C.
  3 only
• D.
  1,2 and 3

Answer 1

The correct option is B

1 and 3 only
Explanation:

Statement 1 is correct: A substance is said to undergo a physical change if only the physical properties such as the substance's form, size, colour, state or appearance change. It remains unchanged as to its chemical composition. Some of the characteristics of a physical change are:

• Temporary in nature.
• Does not affect the internal structure of a substance, only the molecules are rearranged.
• Very little or no energy is released
• No new substance is formed.
• Most of the physical changes are reversible. We can obtain the substance back even after the change.

Statement 2 is incorrect: Physical change involves very little or no energy is released. When the chemical properties of a substance alter, a substance is said to undergo a chemical change. As a consequence, at the molecular level, atomic bonds are either formed or breached. Some of the characteristics of a chemical change are:

• Permanent in nature.
• Since the original composition of the substance changes, one or more new substances are formed.
• Forms of energy, such as heat, light or electricity, may be emitted or absorbed.
• A chemical change is generally irreversible. At least, it cannot be reversed by simple physical means.

Statement 3 is correct: Some of the examples of a physical change are freezing and boiling of water, melting of ice, condensation, magnetizing a compass needle, vaporization, dissolving sugar in water, etc.