CBSE Class 12 · 2022 · d and f Block ElementsShort Answer

(a) Consequences of lanthanoid contraction (any two):

1. The 4d and 5d members of each group (Zr–Hf, Nb–Ta) have almost identical radii, hence almost identical properties — they occur together and are difficult to separate.
2. The basicity of hydroxides decreases regularly from La(OH)${}_3$ to Lu(OH)${}_3$ (smaller Ln${}^{3+}$ → more covalent M–OH).

(Also: the lanthanoids themselves are so alike that separating them requires ion-exchange methods.)
(b) Manganese. With [Ar]3d${}^5$4s${}^2$, all five unpaired d electrons plus the two s electrons can take part in bonding, so Mn shows every state from +2 to +7 — the widest range in the 3d series.