ANS:B - an endothermic reaction.

Cracking is generally considered to be an endothermic reaction. Here’s an explanation:

• Cracking: In petroleum refining, cracking refers to the process of breaking down large hydrocarbon molecules into smaller, more valuable molecules. This is typically achieved by heating the hydrocarbons to high temperatures.
• Endothermic Reaction: An endothermic reaction absorbs heat from its surroundings to proceed. In the case of cracking, the breaking of strong carbon-carbon bonds in larger molecules requires energy input (heat) to break these bonds and form smaller molecules.
• Temperature Dependence: Cracking is favored at high temperatures because higher temperatures provide the necessary energy to break the carbon-carbon bonds efficiently. Therefore, it is not favored at very low temperatures where insufficient energy is available to initiate and sustain the cracking process.
• Practical Application: Industrial cracking processes such as catalytic cracking and steam cracking are carried out at temperatures ranging from several hundred to over a thousand degrees Celsius to optimize the yield of desired products such as gasoline, diesel, and petrochemical feedstocks.