Rubidium
Rubidium forms chemical compounds in only one oxidation state: +1. Some rubidium compounds have a mixed oxidation state, though. Rubidium chloride is the most common rubidium compound. Rubidium hydroxide and rubidium carbonate are also used commonly. Rubidium compounds makes a red-violet color in a flame. Most rubidium compounds are colorless. Rubidium compounds are not as common as other alkali metal compounds, such get sodium compounds. Otherwise, they are similar.