Which substance will have the most heat flow from it?

The choice of the nuclear reactor core as the substance with the most heat flow is based on its significantly higher temperature compared to the other options. Heat flow occurs from a substance at a higher temperature to one at a lower temperature, a concept governed by the second law of thermodynamics.

In this context, the nuclear reactor core operates at approximately 1000°C, which is much hotter than the other substances listed. This extreme temperature creates a substantial thermal gradient, facilitating a significant amount of heat transfer. The stovetop burner, while also hot at 200°C, does not generate nearly as much heat flow as the reactor core due to its lower temperature.

The human body at 36°C and air at room temperature (32°C) represent much cooler temperatures. Heat flow from these substances would be minimal compared to that of the nuclear reactor core, which releases heat at a much higher rate due to the steep temperature difference it creates with its surroundings. When considering heat transfer, the temperature differential is a crucial factor, making the nuclear reactor core the clear choice as the source of the most heat flow in this scenario.