Compare lanthanoids and actinoids with reference to :
(i) the electronic of atoms
(ii) the oxidation states of elements
(iii) general chemical reactivity of elements.

Explanation

(a) Electronic configurations. The general electronic configuration of lanthanoids is `[Xe]4f^(1-14) 5d^(0-1) 6s^2 ` whereas that of actionoids is `[Rn] 5f^(1-14) 6d^(0-1)7s^2` . Thus, lanthanoids involve the filling of 4f-orbitals whereas actinoids involve the filling of 5f-orbitals.
(b) Oxidation states. Lanthanoids have principal oxidation state of +3. In addition, the lanthanoids show limited oxidation states such as +2, +3 and +4 because of large energy gap between 4f and 5d subshells. On the other hand, actinoids show a large number of oxidation states because of small energy gap between 5f and 6d subshells.
( c) Atomic and ionic sizes. Both lanthanoids and actinoids show decrease in size of their atoms or ions in +3 oxidation state. In lanthanoids, the decrease is called lanthanoid contraction and in actinoids, it is called actinoid contraction.
(d) Chemical reactivity. Lanthanoids are highly electropositive in nature and they have almost similar chemical reactivity. All the actinoids are also electropositive and have high reactivity. However, in general, actinoids are more reactive (especially in finely divided state) than lanthanoids.