The property of a body that determines the direction of heat flow when the body is in contact with another body is the

Analyze the question: The question asks which property decides which way heat flows when two bodies touch each other.

Concept: Heat is energy in transit. It always flows spontaneously from a body at a higher temperature to a body at a lower temperature. Heat flow stops when both bodies reach the same temperature, which is called thermal equilibrium.

Checking each option:

• A. Heat capacity: This is the amount of heat needed to raise a body's temperature by 1 K (J/K). It tells you how much heat is needed for a temperature change, not the direction of flow.
• B. Mass: This is the amount of matter in a body. It affects how much heat the body can store, but not the direction of flow.
• C. Power: This is the rate of energy transfer (watts). It has nothing to do with direction.
• D. Temperature: This measures how hot or cold a body is, and it determines the direction of heat flow. Heat goes from the body with the higher temperature to the one with the lower temperature.

A large block of ice has much more mass and heat capacity than a small cup of hot tea. Heat still flows from the tea to the ice, because the tea is at the higher temperature.

Answer: D. Temperature.

Exam tip: Remember "Temperature gives direction, heat capacity gives amount." If a question asks which way heat flows, think temperature difference. If it asks how much heat is needed, think mass, specific heat capacity and temperature change (Q = mcΔθ).