Who were the processing centers for immigrants on the west and east coasts?

Answer 1

The question is possibly misstated. A substance can be either a compound OR a mixture.

A compound is a pure chemical substance consisting of more than one element that can be separated into simpler substances by chemical reaction. The elements are present in a fixed proportion, for example 1 atom of carbon can combine with 2 atoms of oxygen to form carbon dioxide. Compounds have definte properties such as melting points, solid densities, etc. the elements making up the compound do not retain their original properties.

By contrast, a mixture can be separated physically into different components with different properties (while compounds must be separated by chemical means). Conversely, mixtures can be created by mechanical means alone, but a compound can only be created (either from elements or from other compounds, or a combination of the two) by a chemical reaction. A mixture will have multiple properties depending on what part of the mixture you examine - different parts might have different colors, densities, melting points, etc.

Concrete is a composite mixture of cement, sand and (usually) coarse aggregate like gravel or crushed rock. Water is mixed with it and reacts with the cement to form a very hard hydrate. In reality, "wet" concrete is concrete where not all the water has reacted yet. Very little of the water actually evaporates by the time the concrete becomes "dry". The cement in the concrete is a compound. The concrete as a whole is a mixture.