$\begin{array}{1 1} \text{(a) An elements having a completely filled d or f subshell in any common oxidation state.} \\ \text{(b) An elements having a partially filled d or f subshell in any common oxidation state.} \\ \text{(c) An elements having a partially filled s subshell in any common oxidation state.} \\ \text{(d) An elements having a partially filled p subshell in any common oxidation state.} \end{array} $
