Final answer:
The three methods of heat transfer are conduction, convection, and radiation. Conduction cannot take place in a vacuum due to the absence of matter for direct contact.
Step-by-step explanation:
There are three main methods of heat transfer: conduction, convection, and radiation. Conduction is the transfer of heat between two objects in direct contact with each other. Convection is the transfer of heat through the movement of a fluid, such as air or water. Radiation is the transfer of heat through electromagnetic waves, such as sunlight.
Out of these three methods, conduction cannot take place in a vacuum due to the absence of matter for direct contact. In conduction, heat is transferred through physical contact between objects. In a vacuum, there is no material to come into direct contact with, so conduction is not possible.