Kelvin
Explanation
Temperature is a physical quantity that expresses the degree of hotness or coldness of a substance. To ensure uniformity in scientific measurements globally, the International System of Units (SI) establishes standard base units for fundamental physical quantities, including thermodynamic temperature.
Option Analysis
- Degree Celsius is incorrect: Degree Celsius (°C) is a widely used metric unit for temperature in daily life and general scientific contexts. However, it is a derived unit relative to the SI system, defined by the freezing and boiling points of water at standard atmospheric pressure.
- Fahrenheit is incorrect: Fahrenheit (°F) is a temperature scale primarily used in the United States and a few other territories for non-scientific purposes. It is not part of the metric or SI system.
- Kelvin is correct: The Kelvin (K) is the base unit of thermodynamic temperature in the International System of Units (SI). It is an absolute scale where zero (0 K) represents absolute zero, the theoretical point at which particles have minimal thermal motion. Unlike Celsius or Fahrenheit, the unit is written simply as "Kelvin" without the word "degree" or the degree symbol.
- Pascal is incorrect: The Pascal (Pa) is the SI derived unit of pressure, defined as one newton per square metre. It is unrelated to the measurement of temperature.
Key Takeaway: The Kelvin (K) is the fundamental SI unit for thermodynamic temperature, distinct from the Celsius and Fahrenheit scales which are used for practical and historical reasons.