Which temperature scales are used in the SI system?

The Celsius and Kelvin scales are the two temperature scales that are used in the SI (International System of Units) system. The Celsius scale is a metric scale that sets the freezing point of water at 0 degrees and the boiling point at 100 degrees under standard atmospheric conditions. It is widely used around the world for everyday temperature measurements.

The Kelvin scale, on the other hand, is the absolute temperature scale used in science and engineering. It starts at absolute zero, the theoretical point where all thermal motion ceases, which is equivalent to -273.15 degrees Celsius. The Kelvin is primarily used in scientific contexts because it provides a direct relation to the physical behavior of gases and other materials in thermodynamic equations.

This distinction between Celsius for everyday use and Kelvin for scientific accuracy emphasizes why both are included in the SI system, making the first choice the correct answer.

The remaining options do not align with the SI system. Fahrenheit and Rankine are imperial-based scales; Absolute and Adiabatic are not temperature scales; Endothermic and Isothermic refer to processes rather than temperature measurements.