(1) The decrease in ionic radii of the lanthanides from 103 pm (La$^{3+}$) to 86 pm (Lu$^{3+}$) in the lanthanide series.
(2) The Basic nature increases from Ce(OH)$_3$ to Lu(OH)$_3$
(3) The covalent nature in M(OH)$_3$ will decrease from Ce(OH)$_3$ to Lu(OH)$_3$
(4) The E$^{\circ}$ value increases slightly due to Lanthanide contraction
$\begin {array} {1 1}Both (2) and (3) \\ Only (2) \\ Both (1) and (2) \\ (1), (2) and (4) \end {array}$
