Thermal Expansion in Solids

Steps:

• Heat increases the kinetic energy of molecules in the solid.
• Molecules vibrate more intensely around fixed positions.
• Increased vibrations push molecules farther apart on average.
• Overall, the solid expands due to larger intermolecular spaces.

Why A is correct:

• In solids, molecules remain roughly the same size; expansion occurs because thermal energy widens the spaces between them, as per the kinetic molecular theory.

Why the others are wrong:

• B: Molecules do not expand; only spaces increase.
• C: Spaces enlarge, not shrink, during heating.
• D: Spaces do increase, contrary to no change.

Final answer: A