Arrow 4 show convection. Thus option 4 is correct.
What is convection ?
The process in which transfer of heat occurs by movement of a heated fluid either air or water called as convection.
Initially the heat transfer through conduction, however a bulk heat transfer takes place due to the motion of the fluid.
The mechanism of convection involved, fluid is heated from below, leads to thermal expansion.
So that the lower layers, which are hotter now, become less dense.
So the less denser layer replaced by colder layer due to buoyancy nd colder layer is more dense.
This process continuously occur and heat transfer occur through convection
It occurs in both liquid and gases, may be natural or forced, bulk transfer occur.
Thus option 4 is correct.
Learn more about convection, here:
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