Which instrument should be selected to observe temperature accurately?

Correct answer: Thermometer

Temperature tells how hot or cold something is, so the selected instrument must be designed to measure that quantity. A thermometer contains a temperature scale and gives a reading that can be compared with other readings. The observer should use it correctly, place it appropriately, and read the scale carefully. Choosing an instrument according to the quantity being studied is an important part of accurate observation. Different thermometers may be used for different ranges or purposes, but all are intended to measure temperature.

Option B is correct because a thermometer, or तापमापी, is specifically used to measure temperature. A ruler measures length, a balance measures mass, and a measuring cylinder measures liquid volume. None of those instruments directly gives a temperature reading. Therefore, matching the thermometer to the observation required makes B the only suitable option. The word accurately also reminds the student that correct handling and reading are important, not merely naming the instrument.