Explain why stainless steel, sea water, and air are all considered solutions

They are composed by two or more pure substances.

Explanation:

Hello,

At first, we must take into account that mixtures are such materials made up of two or mire pure substances, say elements, molecules or compounds. They are classified as homogeneous for which there is no appreciable difference upon its constituents and as heterogeneous for which the constituents are differentiable. Now, stainless steel is considered as a mixture as long as it is mainly composed by iron and carbon and some other metallic elements such as chromium. Sea water is another interesting example, since the main constituents are water and sodium chloride, nonetheless, other ions such as iodide, sulfate, magnesium (II), potassium (I), calcium (II) are also found into it. Finally, the air is a mixture due to the presence of oxygen and nitrogen as the major constituents, considering others such as carbon dioxide, methane (pollution), argon, hydrogen as traces, it means, compositions below the 1%.

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there is none because earth is stationary and flat.