Rubidium (Rb) is a soft, silvery-white metallic element that belongs to the alkali metal group of the periodic table. It is highly reactive, especially in the presence of water, producing rubidium hydroxide and releasing hydrogen gas. Due to its high reactivity, rubidium is usually stored in mineral oil or in an inert atmosphere to prevent it from reacting with moisture or oxygen in the air. Rubidium has a single naturally occurring stable isotope, Rb-85, but it also has a radioactive isotope, Rb-87, which is used in geology and archaeology for radiometric dating. Additionally, rubidium atoms have been employed in atomic clocks due to their precise resonance frequency, and they've played roles in advanced research areas like Bose-Einstein condensates. Because of its limited abundance and high reactivity, rubidium doesn't have extensive commercial applications, but it's utilized in some specialized areas such as vapor reference cells in atomic physics research.