The differences observed in solids, liquids and gases may be accounted for by

Step 1: Analyze the question The question asks what explains the differences between the three states of matter (solids, liquids and gases), such as shape, volume, compressibility and ability to flow.

Step 2: Explain the concept The kinetic theory of matter says all matter is made of tiny particles (molecules or atoms). The state of a substance depends on two things:

• How far apart the molecules are (spacing)
• How strong the attractive forces between them are (intermolecular forces)

| State | Spacing | Intermolecular forces | Result | |---|---|---|---| | Solid | Very close, in fixed positions | Very strong | Fixed shape and volume | | Liquid | Close, but able to slide past each other | Moderate | Fixed volume, takes the shape of its container | | Gas | Very far apart | Very weak | No fixed shape or volume, easily compressed |

Step 3: Evaluate the options

• A. Relative masses: Mass does not decide the state. A heavy gas such as radon is still a gas, while a light solid such as lithium is still a solid.
• B. Melting points: A melting point is a consequence of the strength of the forces between molecules. It does not explain the differences.
• C. Spacing and forces between the molecules: This is the basic cause of the differences in the states of matter.
• D. Different molecules in each: The same substance, such as water, can be a solid (ice), a liquid or a gas (steam) while keeping the same molecules.

Step 4: Answer The correct option is C.

Exam tip: For any question on "why states of matter differ", think spacing + forces. Water as ice, liquid and steam is a good example to remember: the molecules are the same, but the spacing and forces change.