a
Unlike lanthanides, actinides show a variety of oxidation states from \(+3\) to \(+6\) due to the very small energy gap between \(5 f , 6 d\), and \(7 s\) subshells.

The principal oxidation states are \(+3\) and \(+4\). The \(+3\) oxidation state is the most stable. The \(+4\) oxidation state is the most stable in Th and Pu. \(+5\) in \(Pa\) and \(Np\) and \(+6\) is seen in U. In actinides, the distributions of oxidation states are uneven.