Chlorine and iodine are both elements in the HALOGEN group, which is a group of elements that includes fluorine, bromine, and astatine. Chlorine and iodine are both non-metallic elements with seven protons in their nucleus. Chlorine is a greenish-yellow gas at room temperature, while iodine is a solid at room temperature. Both chlorine and iodine are used in a variety of industrial and medical applications, such as water purification, disinfection, and medical imaging.