Question

Which one of the following lanthanoids does not form $MO_2$? [M is lanthanoid metal]

• A. Pr
• B. Dy
• C. Nd
• D. Yb

Answer 1

Answer: (D)

Yb

Answer 2

Lanthanoids typically exhibit a +3 oxidation state. The question asks which lanthanoid does not form $MO_2$, implying the +4 oxidation state.

1. Pr (Praseodymium): Forms $PrO_2$ (Pr in +4, $4f^1$ configuration).
2. Nd (Neodymium): Primarily +3. +4 state ($4f^2$) is very unstable; $NdO_2$ is not a common stable oxide.
3. Dy (Dysprosium): Primarily +3. +4 state ($4f^8$) is very unstable; $DyO_2$ is not a common stable oxide.
4. Yb (Ytterbium): Primarily +3 and +2 ($4f^{14}$ is stable). The +4 state ($4f^{12}$) is not observed for Yb; hence, $YbO_2$ does not form.

Therefore, Yb is the correct answer as it unequivocally does not form $MO_2$.