Which one of the following lanthanoids does not form ${\mathrm{MO}}_2$? [$\mathrm{M}$ is lanthanoid metal]

$\mathrm{Yb}$ is the only element that does not form ${\mathrm{MO}}_2$ type oxide.

Ytterbium is a soft, malleable and rather ductile element that exhibits a bright silvery luster. A rare earth, the element is easily attacked and dissolved by mineral acids, slowly reacts with water, and oxidizes in air. The oxide forms a protective layer on the surface. Compounds of ytterbium are rare.