Here's why:

* Ionic compound: Copper(II) oxide is an ionic compound, formed by the electrostatic attraction between copper(II) ions (Cu²⁺) and oxide ions (O²⁻).

* Crystal lattice: Ionic compounds typically form a rigid crystal lattice structure.

* Insolubility: Copper(II) oxide is generally insoluble in water. While a tiny amount might dissolve, the majority of it will remain as a solid.

So, while you might see it mixed with water, copper(II) oxide itself doesn't exist as an aqueous solution in the way that something like salt (NaCl) does.