The document discusses four chemical elements: scandium, yttrium, lanthanum, and actinium. It provides details on their discovery, physical and chemical properties, common reactions, useful applications, and health and environmental effects. Scandium was discovered in Sweden in 1879. Yttrium was discovered in Finland in 1794. Lanthanum was discovered in Sweden in 1893. Actinium was discovered in France in 1899. All four elements are metals that react readily with oxygen, halogens, acids and water. Their compounds have applications in lighting, lasers, catalysts, alloys and medicine. Prolonged exposure may cause liver damage and cancer due to their radioactive or toxic nature.