Question

slide 19:what is meant by a phase? slide 20: how many phases in a heterogeneous mixture ( oil, density column)? slide 21: how many phases in a homogeneous mixture?

Explanation:

In chemistry, a phase is a physically distinct form of matter. A heterogeneous mixture has multiple phases as its components are not uniformly distributed. For example, in an oil - density column, oil and other substances form different layers, each a separate phase. A homogeneous mixture has one phase as its components are uniformly distributed throughout.

Answer:

Slide 19: A physically distinct form of matter.
Slide 20: Multiple phases.
Slide 21: One phase.