Answer: Thermal conductivity.
Explanation: In the iron, a piece of metal is heated up, and you put this on top of clothes in order to heat the clothes and remove the wrinkles in it.
Then, the thing that is useful here is amount of heat that the iron transmits to the thing that it touches, and this is directly related to the thermal conductivity, that tell us "how much heat a given material absorbs or transmits (in this case, the metal is hot and the clothes are cold, so the metal piece is transmitting heat)"
Then the correct option is the thermal conductivity
