What is the red liquid in a thermometer?

The red liquid found in a thermometer is typically a non-toxic, alcohol-based liquid called ethanol. This liquid has a low freezing and boiling point, making it suitable for use in thermometers to measure temperature changes. The red color is often added for visibility and to make it easier to read the temperature scale. Ethanol thermometers are commonly used in medical, industrial, and home settings to measure body temperature, room temperature, and other environmental temperatures. It is important to handle thermometers with red liquid carefully to prevent breakage and exposure to the liquid.