Choose the pair from the given options that shows a similar relation as the pair:-

THERMOMETER : TEMPERATURE

Cardiograph : Heart rate

The correct answer is Cardiograph : Heart rate.

In the pair Thermometer : Temperature, a thermometer is an instrument used to measure temperature. Similarly, a cardiograph is an instrument used to measure heart rate.

The other options do not have the same relationship.

• Millimeter : Scale. A millimeter is a unit of length, but a scale can be used to measure different things.
• Length : Breadth. Length and breadth are both dimensions of a shape, but they are not related in the same way as a thermometer and temperature.
• Solar Energy : Sun. Solar energy is the energy that comes from the sun, but it is not measured with an instrument in the same way that temperature is measured with a thermometer.