I think the correct word to fill in the blank would be carbon. Organic compounds are composed of carbon and at least one hydrogen atom. It is basically any compound that would contain carbon and covalently bonded to other elements or atoms usually these are hydrogen, nitrogen and oxygen. All living things are based on these compounds. These are the building blocks of organic chemistry. These compounds can be seen anywhere in Earth. May it be animals, plants, the soil, sugar, microorganisms and even in humans. Examples of these compounds are methanol, DNA, glucose, hexane, acetic acid, butane and the like.