Correct Answer: Thorium

Solution : The correct option is Thorium .

Thorium (Th) is a member of the actinide series. It is located just above uranium in the periodic table and is part of the actinide series due to its electronic configuration and properties associated with the filling of the 5f orbitals. Thorium is a chemical element with the symbol Th and the atomic number 90. It is not as reactive as uranium and tarnishes slowly in the air.