Thermal conductivity is the property of a material that describes its ability to transfer heat through conduction.

The SI unit of thermal conductivity is watts per meter-Kelvin (W/m-K), which represents the amount of heat transferred through a material per unit area and temperature difference.

Copper has the highest thermal conductivity among the given options, making it an excellent conductor of heat.

The relationship between thermal conductivity and temperature can vary depending on the material. In some materials, thermal conductivity increases with increasing temperature, while in others, it decreases or remains relatively constant.

Specific heat is the property of a material that describes its ability to store heat energy per unit mass and temperature change.

The SI unit of specific heat is joules per kilogram-Kelvin (J/kg-K), which represents the amount of heat required to raise the temperature of one kilogram of a material by one Kelvin.

Water has the highest specific heat among the given options, meaning it can store more heat energy per unit mass and temperature change.

The relationship between specific heat and temperature can vary depending on the material. In some materials, specific heat increases with increasing temperature, while in others, it decreases or remains relatively constant.

Emissivity is the property of a material that describes its ability to emit thermal radiation.

A perfect blackbody has an emissivity of 1, meaning it absorbs and emits thermal radiation perfectly.

Rough surfaces generally have higher emissivity compared to smooth or polished surfaces.

The relationship between emissivity and temperature can vary depending on the material. In some materials, emissivity increases with increasing temperature, while in others, it decreases or remains relatively constant.

Thermal expansion is the property of a material that describes its tendency to expand or contract with changes in temperature.

The SI unit of thermal expansion is meters per Kelvin (m/K), which represents the change in length of a material per unit length and temperature change.

Invar is a nickel-iron alloy known for its exceptionally low thermal expansion coefficient.

Generally, thermal expansion increases with increasing temperature for most materials.