Which of the following device is used to measure temperature?

Thermometer

The correct answer is option 2. Thermometer.

The device used to measure temperature is thermometer.

1. Barometer: A barometer is used to measure atmospheric pressure, not temperature. It is particularly useful for weather forecasting.

2. Thermometer: A thermometer is specifically designed to measure temperature. It typically consists of a sealed tube containing a liquid (e.g., mercury or alcohol) that expands or contracts with changes in temperature. The scale on the thermometer provides temperature readings.

3. Polarimeter: A polarimeter is used to measure the optical rotation of polarized light, typically in chemical and pharmaceutical applications. It is not designed for measuring temperature.

Therefore, the correct device for measuring temperature among the options provided is the thermometer.