Question

difference between pyrolysis and cracking

Answer 1

cracking is a chemical reaction ; in case of WMO it is thermal decomposition of long carbon chain to 2w or more chains having lesser number of carbon atoms.

Distillation is a physical separation of different chemical species which is based on the difference in boiling points (and relative volatility) of those species. If any of the species you are trying to distill-off is having higher boiling point than its decomposition temperature then you will first have cracking of that species and then distillation of the resulting products.

Answer 2

^~Yup~^ That would be the right answer :)