Solids expand on heating because
A. the kinetic energy of the atoms increases
B. the potential energy of the atoms increases
C. the potential energy of the atoms decreases
D. the kinetic energy of the atoms increases

Hint: Recall the basics of solids. Recall the process that occurs in atoms of solids when they are heated. Check the heat energy supplied to the atoms of solids gets converted into which type of energy. Hence, determine why the solids expand when they are heated.

Complete answer:
We know that the atoms of the solids are arranged in a regular pattern compactly.
When the solid is heated, the heat which is also a form of energy is gained by the atoms of the solids and this heat energy is transferred to adjacent atoms of the solids by the neighboring atoms.
This heat energy transferred by the atoms in the solids to the neighboring atoms is converted into kinetic energy and due to this kinetic energy the atoms in the solids start vibrating about their mean position.
This vibrations of the atoms of solids about their mean position increases the total volume of the solid.
Hence, the solids on heating expands due to increase in kinetic energy of the atoms.

So, the correct answer is “Option A”.

Note:
The students can also explain the process of expansion of solids using the law of conservation of energy by which the heat energy given to the solids is converted into the kinetic energy because of which the atoms in the solids start vibrating about their mean position and the solids expand on heating.
The solids expand when they are heated. But when the temperature of the solids decreases, the kinetic energy of the atoms decreases resulting in decrease in vibrations of the atoms. Hence, the solids regain its original size when it is cooled.