Which type of copper conductor has the lowest conductivity and highest resistivity?

The type of copper conductor that has the lowest conductivity and highest resistivity is indeed hard-drawn copper. This form of copper is characterized by being drawn through a die to reach a desired diameter without any subsequent annealing process, which would soften it. The rigid structure that results from this process creates increased resistivity due to the lack of free movement for the atoms within the copper.

Hard-drawn copper has a higher tensile strength compared to other forms, which makes it useful for applications where strength is crucial. However, this rigidity also means that the electrons, which are responsible for conduction, encounter more obstacles as they move, hence contributing to higher resistivity and lower conductivity.

In contrast, soft-drawn and annealed copper conductors can attain greater conductivity due to their more flexible atomic structures that allow for easier electron flow. Stranded conductors, while they may be made from hard- or soft-drawn copper, are designed for flexibility and ease of installation, typically sacrificing some properties for versatility. Therefore, it is hard-drawn copper that stands out for having the lowest conductivity and highest resistivity among the provided options.