Krypton (Kr), a noble gas, is sometimes known as the hidden gas because it was so hard to isolate from the air. Scientists, however, have discovered that krypton is useful in many ways. It is used in lighting, lasers, and medicine. It is used to detect leaks in sealed containers and to measure X-rays. Scientists have even used it to determine the age of water locked away in spaces deep underground! In this book, students learn about the periodic law, krypton’s discovery, and krypton’s relationship to the other noble gases. They will explore its atomic structure, how krypton is obtained through fractional distillation, how it forms compounds, and how the gas is used in businesses and industries, including in fluorescent lights, vehicle headlights, neon signs, windows, and insulation.