What is the metric scale of temperature where water freezes at 0 degrees and boils at 100 degrees under standard conditions?

The Celsius scale is a metric system of temperature measurement where specific points are defined for the physical properties of water. Under standard atmospheric conditions, water freezes at 0 degrees Celsius and boils at 100 degrees Celsius. This scale is particularly useful in scientific contexts and is widely adopted in many countries around the world for its straightforward relationship with the physical properties of water, which are familiar and commonly encountered.

The other temperature scales, while they serve their purposes, do not align with this same system. The Fahrenheit scale, primarily used in the United States, sets the freezing point of water at 32 degrees and the boiling point at 212 degrees, which are not metric measurements. The Kelvin scale starts at absolute zero, with water freezing at 273.15 K and boiling at 373.15 K, making it less intuitive for everyday purposes. Similarly, the Rankine scale is an absolute temperature scale used mainly in engineering and thermodynamics, and it also differs significantly from the Celsius scale in its point of reference for freezing and boiling water.

Overall, Celsius is the correct answer because it defines freezing and boiling points of water at 0 degrees and 100 degrees, respectively, creating a direct correlation with water's physical characteristics.