CBSE Class 12 · 2003 · Foreign · d and f Block ElementsVery Short Answer

La(OH)${}_3$ is the more basic.
By the lanthanoid contraction Lu${}^{3+}$ is the smallest ion; its high charge density makes the Lu–OH bond more covalent, holding the OH${}^{-}$ tightly.
La${}^{3+}$, the largest, forms the most ionic M–OH bond, releasing OH${}^{-}$ most readily — basicity decreases from La(OH)${}_3$ to Lu(OH)${}_3$.