Thermal Expansion of Solids

Steps:

• Heating causes atoms in the metal to vibrate more, increasing interatomic distances.
• This expansion leads to an increase in the rod's volume.
• Mass remains constant as no material is added or removed.
• Density, defined as mass/volume, decreases because volume grows while mass stays the same.

Why A is correct:

• Thermal expansion increases volume; density = mass/volume, so with constant mass, density decreases, matching option A.

Why the others are wrong:

• B: Mass does not decrease; it remains constant during heating.
• C: Volume increases, not decreases, due to expansion.
• D: Density decreases, not increases, as volume rises.

Final answer: A