In modern separation techniques, individual lanthanoid elements are primarily separated from their c — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Lanthanoids are extremely difficult to separate chemically because they all exhibit similar chemical properties and a common $+3$ oxidation state. The ion-exchange method utilizes the lanthanoid contraction. Because the crystal ionic radii decrease from $La^{3+}$ to $Lu^{3+}$, the size of their hydrated ions *increases* in the reverse order. This slight but steady variation in hydrated ionic size leads to different affinities for the ion-exchange resin, enabling successful separation.