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The basic unit of thermodynamic temperature in the SI (International System of Units) system is the Kelvin. The Kelvin scale is essential in scientific contexts because it starts at absolute zero, the theoretical point where all molecular motion ceases. This absolute temperature scale provides a consistent and universal measure of temperature, which is crucial for scientific calculations and thermodynamic equations.

The Kelvin is used primarily in scientific applications, as it aligns with the laws of thermodynamics and provides a direct relationship between temperature and energy. While Celsius is a commonly used temperature scale for everyday purposes, it is based on the freezing and boiling points of water and is not used as the fundamental unit in thermodynamic calculations.

In contrast, the other units listed, such as meters (which measure distance) and kilograms (which measure mass), do not pertain to temperature at all. Their inclusion serves to clarify the distinction between different physical quantities in the SI system. Thus, the Kelvin is correctly identified as the fundamental unit of thermodynamic temperature, underscoring its importance in both theoretical and practical applications in thermodynamics.