The +3 ion of which one of the following has half-filled 4f subshell?

Arrange $C{e}^{3+},L{a}^{3+},P{m}^{3+}Ce^\{3+\},\; La^\{3+\},\; Pm^\{3+\}$ and $Y{b}^{3+}Yb^\{3+\}$ in increasing order of their ionic radii

Four successive members of the first-row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionisation enthalpy?

The aqueous solution containing which one of the following ions will be colourless? (Atomic number: Sc = 21, Fe = 26, Ti = 22, Mn = 25)

Which one of the following elements with the following outer orbital configuration may exhibit the largest number of oxidation states?

Which one of the following ions has electronic configuration $[Ar]3d^6[Ar]3d^6$?

The maximum oxidation state exhibited by actinoid ions is

In aqueous solution, $E{u}^{2+}Eu^\{2+\}$ ion acts as

The actinoids showing +7 oxidation state are

Across the lanthanoid series, the basicity of the lanthanoid hydroxides