What's the difference between cracking and pyrolysis?

The difference between Cracking and Pyrolysis in the former is the process of whereby complex organic molecules such as kerogen or long chain hydrocarbon are broken into a simpler molecule while the later is a thermochemical decomposition of organic material at elevated temperature in the absence of oxygen.

The difference between cracking and pyrolysis is that cracking is the breakdown of large organic compounds by use of a catalyst and low temperatures to form fewer different compounds. In Pyrolysis, it's the decomposition of a compound on heating in absence of air.

Remember that rust prevented by placing a sacrificial electrode in electrical contact with the iron. the sacrificial electrode must be composed of a metal that  oxidizes  more easily than iron (that is, it must be below iron in table 18.1).

The answer would be 25.3