What type of fuel is characterized as being inorganic?

The choice of combustible metals as the type of fuel characterized as being inorganic is correct because combustible metals are elements that do not originate from living organisms and are part of the periodic table. Unlike organic materials, which are derived from living or once-living matter, inorganic materials are often composed of minerals and lack carbon-hydrogen bonds.

In contrast, natural gas is a fossil fuel derived from the decomposition of organic matter over millions of years and is therefore organic. Wood, being derived from trees, is also organic in nature, consisting primarily of cellulose and lignin from plant material. Plastic, while synthetic, is made from hydrocarbons that are often derived from organic materials like petroleum products. Thus, combustible metals distinctly represent inorganic fuels that can support combustion under certain conditions.