The correct option is
B Burning in absence of oxygen
Pyrolysis is a thermochemical decomposition of organic material at high temperatures in the absence of oxygen. It involves the change of chemical composition as well as physical state. It is an irreversible process. The process is used heavily in the chemical industry to produce charcoal, activated carbon, to convert biomass into biochar, to turn waste into safely disposable substances.
Thus, the correct answer is option B.