There are total 18 elements in the fifth period of element table. There are total 18 elements in this period out of which rubidium is the smallest and lies at the starting of the fifth period. Unlike other elements of its group , rubidium is an alkali metal and has an oxidation state of +1 which makes it highly reactive. It reacts violently in air and water.
I believe the most active metal in period 5 is rubidium. Rubidium is the first element placed in period 5. It is an alkali metal, the most reactive group in the periodic table, having properties and similarities with both other alkali metals and other period 5 elements.
