Your teacher gives you a black powder. when you dissolve the powder in water, you see red particles that float to the top, black particles that sink to the bottom, and a green liquid. what was the black powder?

Mixture

Explanation:

A mixture is the material which is made up of two or more substances which are different and are physically combined. In mixture, identities of each specie are retained.

Thus, when the black powder is dissolved in water. The constituents of it shows their properties, the res particles float on water and black particles at bottom and turned water to green. Hence, it is a mixture.