Final answer:
The roasting of marshmallows around a campfire involves the transfer of thermal energy by radiation, specifically infrared radiation emitted from the fire to the marshmallow.
Step-by-step explanation:
The transfer of thermal energy involved in the system while sitting around a campfire and roasting marshmallows that is an example of radiation is option C, where thermal energy moves through the air from the flames to the marshmallow. Radiation is the process by which electromagnetic waves carry energy from a hot object, like fire, through space even when there is no material medium, such as air, between them. This process involves the emission of infrared radiation, which is absorbed by nearby objects and is felt as warmth.