Thallium
Thallium is a silvery white metal, which tarnishes in air. The tarnished metal is grey with a blue tinge, somewhat looking like lead.
In its compounds, thallium can be in the +1 and +3 oxidation states. While the lighter metallic members of the group, aluminium, gallium and indium, almost exclusively exhibit oxidation state +3, especially in aqueous solution, the element thallium is more stable in the +1 oxidation state. Oxidation state +3 is oxidizing.
Thallium is a fairly reactive metal, which in contact with hot water forms thallium (I) hydroxide. Thallium (I) hydroxide is purely basic and dissolves in water very well, forming a colorless solution.
Thallium compounds are very toxic. The metal, nor its compounds, usually are not available for the general public.