Answer: Option (b) is the correct answer.
Explanation:
A process in which on heating a fluid (liquid or gas) the hot material (less dense) rises at the top whereas cool material (more dense) sinks at the bottom then this intermixing of materials is known as a convection.
In conduction process, two atoms with different temperature are kept adjacent to each other then heat flows from warmer object to cooler object.
Radiation is the transfer of energy waves which travel through the space. For example, a metal sheet kept under Sun will become warm due to radiations from the Sun.
Transmission is the process of transferring heat from one body to another with the help a medium.
Thus, we can conclude that in the given situation when cooler water near the top sinks and warms then this type of heat transfer is convection.
