The transition metal oxide that most closely resembles copper in both appearance and conductivity is ruthenium dioxide (RuO2).

Here's why:

* Appearance: RuO2 is a dark, metallic-looking solid, similar in color to copper.

* Conductivity: RuO2 is a highly conductive material, exhibiting metallic conductivity. This makes it a valuable component in electronic applications.

While other transition metal oxides can have similar properties, RuO2 stands out for its remarkable resemblance to copper in these two specific areas.