Pyrolysis of methane and ethane respectively are

• Methane pyrolysis is a highly endothermic reaction that requires the addition of heat. This process is endothermic. The molecular bonds between the hydrogen and oxygen molecules in water must be broken by heat. Here, ethane's C-H bond must be broken in order to be converted to ethylene, which requires energy. This reaction is an example of an endothermic one since energy is being absorbed. 

Hence, the correct answer (C). Both are endothermic.