Question

(i) Name the elements of $3d$ transition series which shows maximum number of oxidation states. Why does it show so?
(ii) Which transition metal of $3d$ series has positive $E_{\left(M^{2+}/M\right)}^o$ value and why?
(iii) Out of ${Cr}^{3+}$ and ${Mn}^{3+}$, which is a stronger oxidizing agent and why?
(iv) Name a member of the Lanthanoid series which is well known to exhibit $+2$ oxidation state.
(v) Complete the following equation
$Mn{O}_4^{-}+8H^{+}+5e^{-}⟶$

Answer 1

(i) Manganese ($3d^{5}4s^2$) shows maximum number of oxidation state as its atoms have unpaired electrons in $3d$ orbitals. It shows all the oxidation state from +2 to +7.

(ii) $Cu$ has positive $E_{\left(M^{2+}/M\right)}^o$value, as high energy (${\Delta }_a+{\Delta }_{i}H$) to transform $Cu\left(s\right)$ to $C{u}^{2+}$(aq) is not balanced by hydration enthalpy.

(iii) $M{n}^{3+}$ is stronger oxidising agent as the charge from $M{n}^{3+}$ to $M{n}^{2+}$ results in half filled, $d^5$configuration which has extra stability.

(iv) Europium, ($E{u}^{2+}$) is formed by losing the two $s$ electrons and its ($Xe)f^7$ configuration acounts its formation.

(v) $Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O$