The chapter explains that metals combine with oxygen to form metal oxides, which are basic in nature and generally have high melting points. Calcium is a metal that forms calcium oxide (CaO), which has a very high melting point (2850 K as shown in Table 3.4) and is soluble in water, forming calcium hydroxide. Carbon and silicon are non-metals that form acidic or neutral oxides. Iron oxide is insoluble in water.