Here's why:

* Cobalt oxide (CoO) is formed by the chemical combination of cobalt (a metal) and oxygen (a nonmetal).

* Compounds are formed when two or more elements chemically combine.

* Metals are elements that are typically shiny, malleable, ductile, and good conductors of heat and electricity.

* Nonmetals are elements that lack these characteristics.

While cobalt oxide contains a metal (cobalt), its properties are different from pure cobalt. It's an ionic compound with unique characteristics like being a black solid and having a high melting point.