Hint: Lanthanides and Actinides are elements with unfilled f orbitals. These elements are placed in separate positions in the periodic table. They show variable oxidation states as well.
Complete step by step answer: -The chemistry of actinoids is not so smooth as that of the lanthanides. -Lanthanoids primarily show three oxidation states i.e. +2, +3 and +4. Among these oxidation states, +3 state is the most common. -They display a limited number of oxidation states because the energy difference between 4f, 5d and 6s orbitals is quite large. -On the other hand, the energy difference between 5f, 6d and 7s orbital is very less. Hence, actinoids display a large number of oxidation states. For example, Uranium and Plutonium display +3, +4 , +5 and +6 oxidation states due to small energy gap between 5f and 6d orbitals, while neptunium displays +3, +4, +5 and +7 oxidation states.
Note: The steady decrease in atomic and ionic radii with increase in atomic number of actinide elements that is positive nuclear charge is referred to as actinide contraction and it is analogous to lanthanide contraction.