Correct Answer: A

Rationale: Mercury is the only metal that exists as a liquid at standard room temperature and pressure. It has a melting point of -38.83°C and a boiling point of 356.73°C. Mercury’s unique liquid state arises from weak metallic bonding and relativistic effects that lower its melting point. It has historically been used in thermometers, barometers, and electrical switches, although its toxicity has limited its modern use. Its chemical symbol, Hg, originates from the Latin word 'hydrargyrum', meaning liquid silver. Despite its hazards, mercury’s distinctive physical properties continue to fascinate scientists.

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