Hint: Organic compounds are any chemical compounds that contain carbon-hydrogen bonds in chemistry. Millions of organic compounds have been identified as a result of carbon's ability to catenate (form chains with other carbon atoms).
Organic chemistry is the discipline that studies the properties, reactions, and synthesis of organic compounds. For historical reasons, a few classes of carbon-containing compounds (e.g., carbonate anion salts and cyanide salts) and a few other exceptions (e.g., carbon dioxide) are not classified as organic and are considered inorganic.
The majority of organic compounds contain carbon, hydrogen, and occasionally other elements such as nitrogen, sulfur, oxygen, or phosphorus. Carbon is found in all living organisms, including bacteria. But, Carbon is the basic element of organic compounds. Organic compounds are sometimes classified based on the number of carbon atoms.
A few types of carbon-containing compounds, such as carbides, carbonates (excluding carbonate esters), simple oxides of carbon, and cyanides, are considered inorganic for historical reasons discussed below. Different forms (allotropes) of pure carbon, such as diamond, graphite, fullerenes, and carbon nanotubes, are also excluded because they are simple substances made up of a single element and therefore are not generally considered to be chemical compounds.
Thus, the correct answer is option A: Carbon.
Organic compounds can be classified in several ways. The distinction between natural and synthetic compounds is significant. Organic compounds can also be classified or subdivided based on the presence of heteroatoms, such as organometallic compounds, which contain carbon-metal bonds, and organophosphorus compounds, which contain carbon-phosphorus bonds.