Question

Which one of the following ions is the most stable in aqueous solution?
(At. no. $Ti=22,V=23,Cr=24,Mn=25$ )

• A. $C{r}^{3+}$
• B. $V^{3+}$
• C. $T{i}^{3+}$
• D. $M{n}^{3+}$

Answer 1

Answer: (A)

In aqueous solution the configuration of the ions are following:
$C{r}^{3+}(21)=3d^{3}4s^0\Rightarrow t_{2g}{}^3{e}_g^0$
$V^{3+}(20)=3d^{2}4s^0\Rightarrow t_{2g}{}^2{e}_g^0$
$T{i}^{3+}(19)=3d^{1}4s^0\Rightarrow t_{2g}{}^1{e}_g^0$
$M{n}^{3+}(22)=3d^{4}4s^0\Rightarrow t_{2g}{}^4{e}_g^0$
We know that half-filled and fully filled orbitals are more stable than partially filled orbitals. Hence among the given ions the only ion which occupies halffilled $t_{2g}$ orbitals is Chromium (III) ion.
Note : Although $M{n}^{3+}$ ion has half-filled $t_{2g}$ orbital but there is one more electron filled in $e_g$ orbital which reduces the stability.