Mercury exists in three forms. Which option correctly lists these forms?

• A. Elemental mercury Hg0; inorganic cations Hg+ and Hg2+; organic compounds such as alkyl, aryl, and alkoxyalkyl
• B. Mercury exists only as elemental metal
• C. Mercury exists only as inorganic cations
• D. Mercury exists only as organic compounds

Answer: (A)

Mercury exists in three main forms: elemental mercury (Hg0), inorganic mercury (primarily as Hg+ and Hg2+ salts), and organic mercury compounds (such as methylmercury, ethylmercury, and other carbon- mercury bonds). This grouping reflects how mercury can be found and behave in the environment and in biological systems, with each form having distinct properties, exposure routes, and toxicities. The given option correctly lists these three categories—the elemental metal, the inorganic cations, and the organic compounds—covering the full spectrum of mercury species. The other statements suggest mercury is found only in one form, which is not true because multiple chemical forms of mercury coexist and are important in understanding toxicity and exposure.