Which statement best describes organic substances?

• A. They contain carbon
• B. They are inorganic
• C. They are always synthetic
• D. They dissolve in water

Answer: (A)

The defining idea is that organic substances are carbon-containing compounds. Carbon’s versatility—its ability to form four covalent bonds and build long chains, branched structures, and rings—lets organic chemistry cover a vast range of substances, from fuels and sugars to proteins and plastics. That makes “they contain carbon” the best, most general description. The other statements aren’t reliable descriptors: some carbon-containing compounds are inorganic, so simply “contain carbon” is more accurate; organic substances are not always synthetic since many occur naturally; and whether they dissolve in water varies widely—many organic compounds are nonpolar and only sparingly soluble in water, so dissolution in water isn’t a defining feature.