These compounds are all forms of magnesium that can be found in nature or produced synthetically.

MgO (magnesium oxide) - commonly known as magnesia, this compound is a white solid that occurs naturally as periclase. It is used in a variety of industrial applications, including as a refractory material, in the production of magnesium metal, and as an antacid.

Mg(OH)2 (magnesium hydroxide) - also known as milk of magnesia, this compound is a white solid that is used as an antacid and laxative.

MgCl (magnesium chloride) - this compound is a colorless crystalline solid that is often used in the production of magnesium metal and as a de-icing agent.

Mg3(PO4)2 (magnesium phosphate) - this compound is a white solid that is used as a nutrient supplement in animal feed and fertilizer.

Overall, these magnesium compounds have various uses in industrial, medical, and agricultural applications.