* Compound: A substance formed when two or more different elements are chemically bonded together in a fixed ratio.

* Mixture: A combination of two or more substances where each substance retains its own properties and can be separated by physical means.

Copper sulfate (CuSO₄) is made up of copper (Cu), sulfur (S), and oxygen (O) atoms chemically bonded together in a specific ratio. It has distinct chemical properties different from its individual constituent elements.

You might be thinking of a copper sulfate solution, which is a mixture of copper sulfate dissolved in water. The copper sulfate itself is still a compound, but the solution is a mixture because the water and the copper sulfate are not chemically bonded.