Crude oil fractions burn cleanly, so they make good fuels. Most modern transport use crude oil fractions. Gas and oil are also burnt in central heating homes and in power stations to generate electricity
Often there are alternatives to using crude oil fractions as fuel, e.g. electricity can be generated by nuclear power or wind power there are ethanol powered cars and solar energy can be used to heat water
But things tend to be set up for using oil fractions. For example cars are designed for petrol or diesel and they’re readily available.
Crude oil fractions are more reliable too
As well as fuel crude oil provides the raw material for making various chemicals including plastics, paints, solvents , detergents & lots of medicines
Carbon is so useful because it is mainly carbon
Each carbon atom forms four covalent bonds which can join atoms together in lots of different ways. Carbon can be arranged in chains or rings, they can be linked together with single, double or even triple covalent bonds and can have many other elements bonded onto them
Unlike most other elements carbon can form huge molecules containing hundreds of atoms joined together example the hormone insulin as well as many other different plastics.
Without carbon complicated life forms wouldn’t exist
Most scientists think carbon will run out but no one knows when.