Secondary Standard Temperature Scale
Celsius, Fahrenheit, and Rankine are all examples of primary temperature scales. However, the Kelvin scale is an example of a secondary standard temperature scale.

Explanation:
- Celsius: The Celsius scale is based on the freezing and boiling points of water, where 0 degrees Celsius is the freezing point and 100 degrees Celsius is the boiling point at standard atmospheric pressure.
- Fahrenheit: The Fahrenheit scale is based on a system where 32 degrees Fahrenheit is the freezing point of water and 212 degrees Fahrenheit is the boiling point of water at standard atmospheric pressure.
- Rankine: The Rankine scale is similar to the Fahrenheit scale but uses absolute zero as its starting point, with 0 degrees Rankine being absolute zero.
- Kelvin: The Kelvin scale is the primary temperature scale used in scientific measurements as it is based on absolute zero, the theoretical lowest possible temperature where all molecular motion ceases.

Significance of Kelvin as a Secondary Standard Temperature Scale:
- The Kelvin scale is often used in scientific research and engineering applications where precise temperature measurements are required.
- It is based on the fundamental properties of matter at the atomic level, making it a more reliable and consistent standard for temperature measurements.
- The Kelvin scale is also used in the field of thermodynamics, where absolute temperatures are essential for calculations and analysis.
In conclusion, the Kelvin scale is an example of a secondary standard temperature scale due to its reliance on absolute zero and its widespread use in scientific and engineering disciplines.