Which of the following symbols represents a unit of thermodynamic temperature in the SI unit system?

The correct symbol for a unit of thermodynamic temperature in the International System of Units (SI) is represented by the letter "K," which stands for Kelvin. This unit is used to measure absolute temperature, a critical concept in thermodynamics, as it adheres to the absolute zero reference point.

In the Kelvin scale, absolute zero (0 K) is the point at which all thermal motion ceases, making it a fundamental scale in scientific disciplines that study heat and energy transfer. Unlike other temperature scales such as Celsius or Fahrenheit, the Kelvin scale is an absolute temperature scale and does not use degrees (°), which is why it is simply stated as "K."

The other symbols refer to different units of measurement: "m" is the symbol for meters, a unit of length; "mol" denotes moles, a unit for measuring the amount of substance; and "kg" stands for kilograms, a unit of mass. Each of these plays a crucial role in various physical calculations but does not pertain to thermodynamic temperature. Thus, K is the only symbol among the options that specifically signifies a unit of thermodynamic temperature within the SI unit system.