Final answer:
Crude oil's molecular composition varies significantly based on its source and is made up of a complex mixture of hydrocarbons such as alkanes, alkenes, and aromatics.
Step-by-step explanation:
The exact molecular composition of crude oil can best be described as option (b): it varies widely depending on the source. Crude oil is primarily made up of hydrocarbons, which are molecules containing carbon and hydrogen, varying in lengths, structures, ranging from straight chains to branching chains to rings. The composition includes several thousand organic compounds such as straight-chain alkanes, cycloalkanes, alkenes, and aromatic hydrocarbons. Each geographic source yields crude oil with different characteristics, meaning that crude oil from a place like Texas can have a different composition from oil sourced in Saudi Arabia. This diversity is why the segregation of crude oil during refinery is essential, as it allows for the production of various byproducts with different properties and uses such as gasoline, diesel, and other petrochemicals.