Hg, or Mercury, is a chemical element with the symbol Hg and atomic number 80. It is a heavy, silvery-white liquid metal at room temperature, known for its high density and ability to conduct electricity. Mercury is unique among metals as it remains liquid in its elemental form, making it useful in thermometers, barometers, and other scientific instruments. Mercury is toxic and can pose serious health risks if inhaled or ingested. It occurs naturally in the environment, often found in ores and released through industrial processes. Due to its harmful effects, many countries have implemented regulations to limit mercury use and exposure.