Which statement correctly describes what happens when two objects at different temperatures are placed together?

• A. Heat flows only if the objects are identical in composition.
• B. Heat flows from the colder object to the hotter object until both reach the same temperature.
• C. Heat flow stops when the objects touch.
• D. Heat flows from the hotter object to the cooler object until both reach the same temperature.

Answer: (D)

When two objects have different temperatures, energy moves as heat from the hotter one to the cooler one. This transfer continues until they both reach the same temperature, at which point there is no net heat flow—thermal equilibrium.

That makes the statement about heat flowing from the hotter object to the cooler object until both reach the same temperature the best description. The other ideas aren’t correct because heat transfer depends on the temperature difference, not on identical composition; heat does not flow from cold to hot, and touching doesn’t by itself stop heat flow—it stops only when the temperatures become equal or when insulation prevents further transfer.