Why can you not fill up a fuel tank with coal?

You cannot fill up a fuel tank with coal because fuel tanks are designed to hold liquid fuels, such as gasoline or diesel, which can flow and be pumped efficiently into engines. Coal is a solid and does not possess the necessary properties to be transported or stored in liquid fuel systems. Additionally, coal requires a different combustion process and is typically used in power plants or for heating, rather than in vehicles designed for liquid fuels.