Combustion reactions use which element as a reactant?

Explanation:

The chemical combustion reactions use a compound called fuel (containing carbon and hydrogen atoms, example: CH4 methane) and oxygen, generating C02 (carbon dioxide) and H20 (water).

Oxygen

Explanation:

Especially hydrocarbons react with oxygen to produce carbon dioxide and water

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.

atomic number of carbon is 6

electronic configuration of carbon is 1s²2s²2p²

orbital diagram of c is as shown here in the image.