WAEC 2011 Physics · Question 32

Which of the following statements is not correct?

Options

A.molecules of ice, water and water vapour have equal intermolecular distances
B.molecules of ice, water and water vapour do not differ in the structure of their molecules
C.molecules of water vapour attract each other with forces far less than the forces of attraction between water molecules
D.water is less compressible than water vapour

Answer: A. molecules of ice, water and water vapour have equal intermolecular distances

Explanation written with AI and checked against the answer key

Analyze the question: We need the statement that is NOT correct about the three states of water (ice, liquid water, water vapour).

Concept: The three states differ in how the molecules are arranged and how far apart they are, but the molecules themselves are the same (H₂O).

Solid (ice): molecules closely packed, strong forces, fixed positions.
Liquid (water): molecules close, but free to slide past each other, with strong forces.
Gas (vapour): molecules very far apart, with very weak forces, and it is highly compressible.

Check each option:

A. Equal intermolecular distances: This is false. In water vapour the molecules are far apart, much farther than in ice or liquid water. Even ice and liquid water differ slightly (ice is less dense because of its open hexagonal structure). So this statement is not correct.
B. No difference in molecular structure: True. Every molecule is H₂O in all three states. Only the arrangement and motion change.
C. Vapour attraction far weaker than in water: True. Large spacing means very weak intermolecular forces in vapour.
D. Water is less compressible than vapour: True. Liquids are nearly incompressible, whereas gases are easily compressed.

Answer: The statement that is not correct is A.

Exam tip: For "which is NOT correct" questions, test each option separately. Remember the order of intermolecular spacing: solid ≈ liquid ≪ gas. Any statement saying the distances are "equal" across states is almost always the false one.

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