Which element is classified as an alkali metal? Rb Sr Zr Cl

From the given options, rubidium (Rb) is an alkali metal. Alkali metals are those that are found in the first group of the periodic table. They are highly reactive, electropositive, have one valence shell electron and form stronly alkaline solutions when they are dissolved in water. Other examples of alkali metals are lithium, sodium and potassium.