The correct answer to the question will be D). Liquids and gases.
EXPLANATION:
Convection is the type of mode of heat transfer in which there will be actual motion of particles from one part to the another part of a fluid.
In case of liquids, the particles which are present at the bottom of the container get heated up first and become lighter. The lighter particles will go up and the top heavier particles will move downward. Again the same process will be repeated. In this way, a convection cycle is produced.
For instance, heating of water.
In case of gases, same thing happens just like liquid. The air particles will be heated up first and becomes lighter. These heated particles will move upward. Due to this, an empty space will be created in that region. In order to occupy the empty space, the air will flow from another region which is at low temperature as compared to the heated region. Again, the same process will be repeated which will results into the formation of convection cycle .
Hence, convection occurs both in liquids and gases.
