Question

Which is the strongest base among the following?

• A. $La(OH{)}_3$
• B. $Lu(OH{)}_3$
• C. $Ce(OH{)}_3$
• D. $Yb(OH{)}_3$

Answer 1

The correct option is A $La(OH{)}_3$

Due to the lanthanoid contraction, the size of the tripositive lanthanoid ion $\left(M^{3+}\right)$ regularly decreases with increase in atomic number, i.e., from $L{a}^{3+}$ to $L{u}^{3+}$. It results in decrease of basic character from $L{a}^{3+}$ to $L{u}^{3+}$. The ionic character of the M-OH bond decreases and the covalent character of the M-OH bond gradually increases.

Therefore, the basic strength of the corresponding hydroxides decreases from $La(OH{)}_3$ to $Lu(OH{)}_3$. Therefore, $La(OH{)}_3$ is the strongest base.