How many methods of heat transmission (transfer) are there?

Heat can be transferred from one place to another by different mechanisms. Option A (2) is incorrect — heat transfer does not occur by just 2 methods. While students sometimes think only of conduction and convection, there is an essential third method. Option B (3) is CORRECT — heat is transferred by exactly 3 methods: (1) Conduction — transfer of heat through direct contact without actual movement of molecules from one place to another. Occurs mainly in solids. (2) Convection — transfer of heat through the actual movement of heated molecules/fluid from one place to another. Occurs in liquids and gases. (3) Radiation — transfer of heat without any material medium, in the form of electromagnetic waves. Can occur through vacuum. All three methods are important for competitive exams. Option C (4) is incorrect — there is no fourth standard method of heat transfer in classical physics. Some advanced texts mention 'advection' as a sub-type of convection but in standard competitive exam curriculum, only 3 are recognized. Option D (5) is incorrect — five methods of heat transfer do not exist in standard physics. The three methods (conduction, convection, radiation) are universally accepted in all syllabi for government competitive exams.