Carbohydrates are organic compounds that consist of carbon, hydrogen, and oxygen in a 2:1 ratio, with the general formula (CH2O)n. This means that for every one carbon atom, there are two hydrogen atoms and one oxygen atom. This ratio is essential for the formation of carbohydrates, which include sugars, starches, and cellulose. Lipids, proteins, and nucleic acids do not have this specific ratio of H and O atoms, making carbohydrates the correct answer.