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Answer:
The concentration of a chemical substance expresses the amount of a substance present in a mixture.
Another definition is that concentration is the ratio of solute in a solution to either solvent or total solution. Concentration is usually expressed in terms of mass per unit volume.
They are called magnets poles.
The oldest lunar rock samples are approximately 4.4 billion years old and composed of anorthosite, a mineral that crystallizes and rises to the top of a lava ocean.