Which of the following thermometers measures temperature from the thermal radiation emitted by objec

A pyrometer measures temperature without touching the object. It collects the thermal radiation (heat and light) the object gives off and works out the temperature from its intensity or colour. This makes it ideal for very hot things such as furnaces and molten metal.

A thermocouple needs two metal junctions in contact with the object. A platinum resistance thermometer measures the change in resistance of a platinum wire. A constant pressure gas thermometer follows the expansion of a gas. All of these must touch what they measure.