In the molecular explanation of conduction, heat is transferred by the

Step 1: Analyze the question The question asks which particles carry heat in the molecular (microscopic) explanation of conduction, mainly in metals, which are the best conductors.

Step 2: Explain the concept Conduction is heat transfer through a material without the material itself moving. There are two mechanisms:

1. Lattice vibrations: In all solids, hot particles vibrate more vigorously and pass the energy on to their neighbours. This is the main mechanism in non-metals.
2. Free electrons: Metals have a "sea" of delocalised (free) electrons. When one end is heated, these electrons gain kinetic energy, move rapidly through the metal, and collide with atoms and other electrons. They carry energy to the cooler parts very quickly.

This is why metals such as copper and aluminium conduct heat much better than wood or plastic, which have few or no free electrons.

Step 3: Solve by checking the options

• A. Free electrons: Correct. They are the charge and energy carriers in the molecular explanation of conduction.
• B. Free atoms: Atoms in a solid are fixed in position in the lattice. They vibrate but are not free to move.
• C. Free molecules: Free-moving molecules describe convection in fluids (liquids and gases), not conduction in solids.
• D. Free solids: This is meaningless in this context.

Step 4: Answer Heat is transferred in conduction by free electrons, which is option A.

Exam tip: Remember the trio:

• Conduction → electrons and vibrating particles (solids)
• Convection → moving fluid molecules (liquids and gases)
• Radiation → electromagnetic waves (no medium needed)

If you see "free electrons" in a conduction question, it is almost always the right choice.