Question

Which one of the following does not correctly represent the correct order of the property indicated against it ?

• A. Ti < V < Cr < Mn : increasing number of oxidation states
• B. $Ti^{3+} < V^{3+} < Cr^{3+} < Mn^{3+}$ : increasing magnetic moment
• C. Ti < V < Cr < Mn : increasing melting points
• D. Ti < V < Mn < Cr : increasing secondion isation enthalpy

Answer 1

Answer: (C)

(A) Element Oxidation states Ti +2, +3, +4 V +2, +3, +4, +5 Cr +1, +2, +3, +4, +5, +6 Mn +1, +2, +3, +4, +5, +6, +7 $\therefore $ order o f oxidation states is : Ti < V < Cr < Mn. (B) Magnetic moment, $\mu= \sqrt{n ( n+2)}$ where $n$ number of unpaired electrons Element Outermost electronic No. of unpaired arrangement electrons $Ti^{3+}$ $3d^1$ 1 $V^{3+}$ $3d^2$ 2
$Cr^{3+}$ $3d^3$ 3
$Mn^{3+}$ $3d^4$ 4
$\therefore $ order o f magnetic moment : $Ti^{3+} < V^{3+} < Cr^{3+} < Mn^{3+}$
(C) In $3d$-series melting point increases as we move from left to right. But Mn shows low melting point due to its complex form ing nature it is unable to form metallic and covalent bonds.
(D) Element Second ionisation enthalpy
Ti 1320
V 1376
Mn 1513
Cr 1635
$\therefore $ order of second ionisation enthalpy is : Ti < V < Mn < Cr.