The document discusses the basic concepts of chemistry and the composition of matter. It explains that all matter is made up of chemical elements, which can exist in solid, liquid, or gas states. The human body contains 26 main elements that are classified into major elements, minor elements, and trace elements. Major elements like oxygen, carbon, hydrogen, and nitrogen make up 96% of body mass, while minor elements like calcium and phosphorus make up 3.8%. The remaining 0.2% consists of trace elements that have important functions, though some of their functions remain unknown.