The valency shell electronic configuration of Cr and Cu atoms, respectively, are

Identify all the correct statements for lanthanoide contraction.

(A) The covalent properties of the lanthanoide metal hydroxides increases from La to Lu.

(B) The chemical reactivity decreases from La to Lu.

(C) $\mathrm{La}(\mathrm{OH})_3$ is more basic than $\mathrm{Lu}(\mathrm{OH})_3$.

(D) Zr and Hf have about the same radius.

(E) Separation of lanthanoides from one another is easy.

The correct order of the electron gain enthalpy of the given elements is

The correct pair of species with $(A)$ the highest bond order and ( $B$ ) diamagnetic character is