Why water is a compound but air is a mixture?

For the following, determine the type of reaction and then give products.

Write the empirical chemical formula of calcium with a mass percent of 38.8, phosphorus with a mass percent of 20.0, and oxygen with a mass percent of 41.3.

Which of the following is most likely true about water in chemical systems? a) water dissolves nonpolar ionic compounds. b) water dissociates ionic compounds. c) water dissociates covalent molecules. d) water dissolves nonpolar covalent substances.