Concept:A mixture contains two or more substances that are not chemically combined.Explanation:Air is a mixture of gases like nitrogen and oxygen.Milk is a mixture of water, fats, and proteins.Cement is a mixture of compounds such as calcium silicates and aluminates.Mercury is a pure element with the symbol Hg and atomic number 80.Since mercury is not made of two or more substances chemically or physically combined, it is not a mixture.Answer:B. Mercury