From the information given in the question, we can infer that we need to check for such a relationship where the instrument is being used to measure the physical quantity. ( since Barometer is being used to measure atmospheric pressure.) In option A, the unit of force is given as kg, which is not a correct relationship. Richter scale is used to measure the strength of earthquakes, but in the option, it is linked to heat. Therefore, option B is not correct. The weighing scale measures the weight of an object, whose unit is Kg. Hence, this is wrong. The thermometer measures temperature, which is the correct relationship. The correct option is D.