Which heat transfer mechanism requires molecules to actually touch each other? radiation, conduction ,convection ,none of these

Option (b) is the correct answer.

Explanation:

When we place two objects of different temperature adjacent to each other then there will occur transfer of heat from hotter object to colder object till their temperature becomes equal.  

This process is known as conduction.

For example, a metal spoon placed in hot coffee cup then heat will flow from coffee to the cup.

On the other hand, convection is defined as the process in which a fluid (liquid or gas) when heated then more dense (cooler) substance sinks ate the bottom whereas less dense (hotter) substance will rises at the top.

For example, boiling water represents convection process.

Radiation is defined as an electromagnetic energy which travels in space in the form of waves or particles.

For example, heating of a metal plate placed in the sunlight.

Thus, we can conclude that conduction is the heat transfer mechanism which requires molecules to actually touch each other.