The Correct Answer and Explanation is:
The correct answer is Mercury.
Mercury, with the chemical symbol Hg, is the group 12 metal that fits this description. It holds a unique position among metallic elements because it is the only one that exists as a liquid at standard temperature and pressure. This distinct physical property, combined with its consistent and significant rate of thermal expansion, made it an ideal substance for use in thermometers for many years. The liquid metal’s opaque, silvery appearance was easy to see and read within the narrow glass capillary of a thermometer, and its high boiling point allowed it to measure a wide range of temperatures accurately.
Despite its utility, the use of mercury in common household items like thermometers has been largely discontinued due to its high toxicity. Mercury is a potent neurotoxin, meaning it can cause severe damage to the brain, spinal cord, and nervous system. Exposure can occur through the inhalation of its vapor, which is continuously released from the liquid at room temperature, or through absorption following direct contact. If a mercury thermometer breaks, it can release this toxic vapor into an enclosed space, posing a significant health risk to anyone nearby. The environmental impact is also a major concern, as spilled mercury can contaminate soil and water, eventually entering the food chain and accumulating in fish and wildlife.
Because of these substantial health and environmental risks, regulations have been implemented worldwide to phase out mercury-containing products. Thermometers are now typically made with safer alternatives, such as alcohol dyed red or blue for visibility, or with digital sensors that provide fast and accurate readings without the use of hazardous materials. This shift away from mercury reflects a greater global emphasis on public safety and environmental protection.
