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

• A

  $\mathrm{Ti} < \mathrm{V} < \mathrm{Cr} < \mathrm{Mn}$ : increasing number of oxidation states
• B

  $\mathrm{Ti}^{3+} < \mathrm{V}^{3+} < \mathrm{Cr}^{3+} < \mathrm{Mn}^{3+}$ : increasing magnetic moment
• Correct answer
  C

  $\mathrm{Ti} < \mathrm{V} < \mathrm{Cr} < \mathrm{Mn}$ : increasing melting points
• D

  $\mathrm{Ti} < \mathrm{V} < \mathrm{Mn} < \mathrm{Cr}$ : increasing second ionisation enthalpy

Solution

$\therefore$ Order of oxidation states is $$ \mathrm{Ti} < \mathrm{V} < \mathrm{Cr} < \mathrm{Mn} $$ (b) $\because$ Magnetic moment, $\mu=\sqrt{n(n+2)}$ where, $n=$ no. of unpaired electrons
$\therefore$ Order of magnetic moment is $$ \mathrm{Ti}^{3+} < \mathrm{V}^{3+} < \mathrm{Cr}^{3+} < \mathrm{Mn}^{3+} $$ (c) In 3 -series melting point increases as we move from left to right. But Mn shows low melting point due to its complex formating nature. It is unable to form metallic and covalent bonds. (d)
$\therefore$ Order of second ionisation enthalpy is $$ \mathrm{Ti} < \mathrm{V} < \mathrm{Mn} < \mathrm{Cr} $$

Hence, the correct answer is option: 'C'.