Which type of heat transfer takes place by actual physical contact, from molecule to molecule, without displacing the molecules?

The correct choice is conduction, as it specifically refers to the transfer of heat through direct contact of particles in a material. When molecules collide with one another, they transfer energy through their interactions. This process occurs without the overall movement of the material itself; instead, it relies on the vibration and movement of the molecules in close proximity.

For example, if you heat one end of a metal rod, the molecules in that heated section vibrate more quickly and collide with neighboring, cooler molecules. This energy transfer continues along the rod until the heat evenly distributes throughout.

Convection, on the other hand, involves the transfer of heat through the movement of fluids (liquids or gases). This process requires the actual movement of the fluid, as warmer areas rise and cooler areas sink. Radiation pertains to heat transfer through electromagnetic waves and does not require a medium, meaning it can occur even in a vacuum. Induction is a method of heating through electromagnetic fields and does not involve direct contact between heat source and material. Understanding the distinctions among these processes highlights why conduction is specifically characterized by heat transfer through direct contact.