Thermal conductivity:
Thermal conductivity is a property that describes the ability of a material to conduct heat. It is defined as the amount of heat that can be conducted through a unit area of a material in a unit time when there is a unit temperature gradient across the material. The SI unit of thermal conductivity is Jm-1s-1K-1. Let's break down this unit and understand its components.

Explanation:
- The SI unit for heat is Joule (J), which is the unit of energy. In this case, we are measuring the amount of heat conducted, so the unit is J.
- The unit of length is meter (m), which represents the unit area through which heat is conducted. Since thermal conductivity is measured per unit area, the unit is m-1.
- The unit of time is second (s), which represents the unit time in which heat is conducted. Again, since thermal conductivity is measured per unit time, the unit is s-1.
- The unit of temperature gradient is Kelvin (K), which represents the difference in temperature across the material. The unit is K-1.

Combining the units:
To calculate thermal conductivity, we need to divide the amount of heat (J) by the product of the area (m2), time (s), and temperature gradient (K). This gives us Jm-2s-1K-1. However, since thermal conductivity is measured per unit area (m-2), we can simplify the unit to Jm-1s-1K-1.

Conclusion:
The SI unit of thermal conductivity is Jm-1s-1K-1, which represents the amount of heat that can be conducted through a unit area of a material in a unit time when there is a unit temperature gradient across the material.