SO they don't rust.
To protect the metal from rust on a steel car. On an aluminum, or carbon fiber car it is not necessary to paint the car. As an example all DeLorean's were not painted from the factory as the body panels were made of aluminum.
Cars were traditionally made out of steel and aluminum, but it is much more common to see cars with an abundance of fiberglass or plastic body panels.
Anderson shelters were made of corrugated iron and Morrison shelters were made from steel panels.
Apart from a few unusual cars that have body panels made of plastic, aluminum or another metal, the vast majority of cars have body parts made from mild steel sheeting. Mild steel is mostly made from iron with a tiny amount of carbonmixed in it. If too much carbon is in the steel it becomes very brittle. Too little or none at all and it becomes too soft. In mild steel around 0.1 - 0.5% is carbon which keeps the steel strong without it becoming brittle.
In batteries the plates are made of lead. Body panels are often made of the compounds steel or carbon fibre. Some manufacturers use body panels that are made from the element Aluminum.
The most widely used material are various steel alloys, but there are options. Some cars may have hoods/bonnets, and even body panels out of plastics. Some are made partly of aluminium.
Most of them are not painted they are wrapped!
Because they have solar panels
Yes, they can.
No, he painted on wood panels.
A painted steel bowl is oven safe, as long as the paint is enamel.