The first 20 element, atomic number and symbols

The atomic nucleus made up from protons (yellow) and neutrons (blue) and held together by nuclear forces. nuclear forces (also known as nuclear interactions or strong forces) are the forces that act between two or more nucleons. they bind protons and neutrons (“nucleons”) into atomic

Answer; carbon monoxide (co);

Combustion is the act or process of burning. therefore, i believe the answer is  a: burning wood.