Question

In context of the lanthanoids, which of the following statements is not correct?

• A. There is a gradual decrease in the radius of the members with increasing atomic number in the series
• B. All the members exhibit $+3$ oxidation state
• C. Because of similar properties the separation of lanthanoids is not easy
• D. Availability of $4 f$-electrons results in the formation of compounds in $+4$ state for all members of the series

Answer 1

Answer: (D)

(a) There is a gradual decrease in the radius of the lanthanoids with increasing atomic number$-a$ case of lanthanide contraction. Thus, true.
(b) Ionisation potential for the formation of $Lu ^{3+}$ is comparatively low, hence $+3$ oxidation state is favourable. Thus true.
(c) Due to lanthanide contraction, $Zr$ and $Hf, Nb$ and $Ta, Mo$ and $W $ have the same size and thus similar properties and thus separation is not easy. Thus true.
(d) Formation of $+4$ state requires very high energy, thus incorrect.