Answer: Option (a) is the correct answer.
Explanation:
A process in which a fluid (liquid or gas) upon heating shows that hot material (less dense) rises at the top and cooler material (more dense) sinks at the bottom leads to generation of convection currents. This process is known as convection current.
Since, particles of gas and liquids are able to move away easily. Hence, they show convection process.
On the other hand, in solids particles vibrate around fixed positions and they have fixed volume. Whereas plasma is the state of matter which contains charged particles.
Thus, we can conclude that gases and liquids both transmit heat by convection because their particles are free to move away from each other.
