Exploring the extreme chemical reducing and oxidizing characteristics of inner transition elements ( — d and f Block Elements Chemistry Question

💡 Solution & Explanation

$Cr^{2+}$ ($d^4$) oxidizes easily to the highly stable $Cr^{3+}$ ($t_{2g}^3$ in water), making it a strong reducing agent. Europium ($Eu$, $Z=63$) forms a $Eu^{2+}$ ion with a stable half-filled $4f^7$ configuration, but the universal stable state for lanthanides is $+3$, so it strongly gives up an electron (reduces others) to become $Eu^{3+}$. Cerium ($Ce$, $Z=58$) forms $Ce^{4+}$ ($4f^0$), but strongly desires the generic $+3$ state, powerfully stripping electrons from other species (oxidizing agent). $Lu^{3+}$ has a closed $4f^{14}$ shell and is incredibly stable; it does not disproportionate.