Among the given elements: - Eu (Europium), Er (Erbium), Tb (Terbium), Yb (Ytterbium), and Lu (Lutetium) all belong to the lanthanoid series. Cm (Curium) belongs to the actinide series.
Hence, the number of elements that do not belong to lanthanoids is 1 (Cm).
For the reaction, \[ H_2(g) + I_2(g) \rightleftharpoons 2HI(g) \]
Attainment of equilibrium is predicted correctly by: