Beryllium is a chemical element with the symbol Be and atomic number 4. It is a lightweight metal that is known for its high strength and low density. Beryllium is commonly used in various industries, including aerospace, electronics, and nuclear reactors, due to its excellent thermal and electrical conductivity. It is also used as an alloying agent to improve the properties of other metals. Therefore, the correct answer for this question is Beryllium, as it accurately represents the element being referred to.