Question

Why basic character in lanthanoid hydroxides decreases across the period?

Answer 1

Basic character of the lanthanoid hydroxides

decreases from $C{e}^{3+}$ to $L{u}^{3+}$ because of

the decrease in the ions from $c{e}^{3+}$ to $L{u}^{3+}$

The covalent character of M-OH bond increase

and hence the basic strength decreases

$\therefore Ce(OH{)}_3\equiv$ most basic

$Lu(OH{)}_3\equiv$ least basic