Which of the following is a physical change? a newspaper burns when placed in a fire. an iron chair rusts when left outside. a sample of water boils and releases gas. a plant changes carbon dioxide and water into sugar. question 3(multiple choice worth 2 points) which of these statements best describes the relationship between elements, compounds, and pure substances? pure substances can be divided into two groups: elements and compounds. compounds can be divided into two groups: pure substances and elements. elements and pure substances are two of many different types of compounds. pure substances and compounds are two of many different types of elements.