Which liquid is used in a liquid thermometer?

Liquid thermometers use specific liquids that show significant change in volume with temperature change. Option A (Water) is incorrect — water is not suitable for thermometers because it has a narrow liquid range (0°C to 100°C), a high surface tension, it is transparent making it hard to read, and most importantly it does not contract or expand uniformly. Option B (Alcohol or Mercury) is CORRECT — two main liquids are used in thermometers: Mercury and Alcohol. Mercury is used for high temperature ranges because it remains liquid from -39°C to 357°C and is opaque (easy to read). Alcohol is used for low temperature measurements because it freezes at around -114°C. Option C (Glycerin) is incorrect — glycerin is a viscous liquid with a high boiling point, not used in standard thermometers due to its high viscosity and non-uniform expansion. Option D (Kerosene) is incorrect — kerosene is flammable and does not expand uniformly with temperature change, making it unsuitable for thermometers. Mercury and alcohol thermometers are the most common types tested in competitive exams.