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. $Cr^{3+}$
• B. $V^{3+}$
• C. $Ti^{3+}$
• D. $Mn^{3+}$

Answer 1

Answer: (D)

$Mn^{3+}$

Answer 2

Stability of transition metal ions is directly proportional to the unpaired electrons. The exactly half-filled and completely filled d-orbitals are extra stable. $Cr^{3+}(21)=3d^3,4s^0$ (3 unpaired electrons) $V^{3+}(20)=3d^2,4s^0$ (2 unpaired electrons) $Ti^{3+}(19)=3d^1,4s^0$ (1 unpaired electron) $Mn^{3+}(22)=3d^4,4s^0$ (4 unpaired electrons) So, $Mn^{3+}$ ion is most stable in aqueous solution.