Which of the following is used as a substitute of mercury in thermometers?

Galinstan

The correct answer is option 3. Galinstan.

Galinstan is a substance used as a substitute for mercury in thermometers.

Galinstan is an alloy composed of gallium, indium, and tin. The name "Galinstan" is derived from the symbols of its constituent elements (Ga, In, Sn). The typical composition is approximately 68.5% gallium, 21.5% indium, and 10% tin by weight.

Galinstan is a liquid metal alloy at room temperature. It remains in liquid form within a wide temperature range, from approximately -19°C (-2.2°F) to 1300°C (2372°F). This wide liquid range makes it suitable for use in thermometers that need to measure temperatures within this range.

Unlike mercury, which is toxic and poses health and environmental risks if mishandled or released, galinstan is considered non-toxic. It is safe to handle and does not present the same hazards associated with mercury exposure.

Galinstan is also more environmentally friendly than mercury. In the event of breakage or spillage, galinstan does not pose the same risks of contamination to soil, water, or air as mercury does. Its use contributes to safer and more sustainable practices in laboratory and industrial settings.

Galinstan exhibits good thermal conductivity and low viscosity, which are desirable properties for accurate temperature measurement in thermometers. It provides reliable and precise temperature readings, comparable to those obtained with mercury thermometers.

Galinstan is used in various applications where a non-toxic, low-melting-point liquid metal is required. Apart from thermometers, it is used in medical devices, electronics, heat transfer systems, and experimental research.

In summary, galinstan is a liquid metal alloy composed of gallium, indium, and tin, used as a substitute for mercury in thermometers and other applications. Its non-toxicity, environmental friendliness, and thermal properties make it a suitable alternative to mercury, especially in situations where safety and accuracy are paramount.