Answer ; Pressure and heat turned plants into a substance now known as coal. Coal is considered an energy source because it takes lots of of years to form.
Coal is formed under the ground when pressure is high and there is a lot of heat also to make coal you need dead and composed organisms put together all of this makes a lump of dark coal.
The atomic number is equal to the number of protons in an atom's nucleus. Hydrogen's atomic number is 1 because all hydrogen atoms contain exactly one proton.
