KnowHOW team explains: Burning or combustion is a reaction, or a set of complex reactions, in which a substance combines with oxygen, producing heat, light and flame. In case of grass, leaves or any other vegetable matter, the basic constituent is carbon. When these things burn, carbon dioxide is produced.

An abundance of oxygen is imperative for any substance to burn. In fact, an important property of the gas is that it supports combustion. However, supporting combustion does not imply that it burns itself. There is a difference between being a supporter of combustion and a combustible substance. Hydrogen, for example, does not support combustion but is a highly explosive gas and burns with a pop. There are other organic chemicals ? mainly those comprising six carbon atoms and a structure resembling a closed-ring ? which are inflammable.

Dry leaves, brush, grass and so on are basically storehouses of waste matter produced by plants in various metabolic processes like respiration and excretion.These metabolites are inflammable organic substances like tannins, hydrogen cyanide or prussic acid and a highly volatile vapour (aromatic in nature). This explains that despite sufficient amount of oxygen being present both in case of green and dry gas, the latter burns more easily.

The question was sent by S. Anantha from Jamshedpur