Question

Which of the following arrangements does not represent the correct order of the property stated against it?

• A. $N{i}^{2+}<C{o}^{2+}<F{e}^{2+}<M{n}^{2+}$ : Ionic size
• B. $C{o}^{3+}<F{e}^{3+}<C{r}^{3+}<S{c}^{3+}$ : Stability in aqueous solution
• C. $Sc<Ti<Cr<Mn$ : Number of oxidation states
• D. $V^{2+}<C{r}^{2+}<M{n}^{2+}<F{e}^{2+}$ : Paramagnetic behaviour

Answer 1

Answer: (B), (D)

The correct options are
B $C{o}^{3+}<F{e}^{3+}<C{r}^{3+}<S{c}^{3+}$ : Stability in aqueous solution
D $V^{2+}<C{r}^{2+}<M{n}^{2+}<F{e}^{2+}$ : Paramagnetic behaviour

The exothermic hydration enthalpies of the given trivalent cations are:
$S{c}^{+3}=3960kJ/mole$
$F{e}^{+3}=4429kJ/mole$
$C{o}^{+3}=4653kJ/mole$
$C{r}^{+3}=4563kJ/mole$
Hence, $S{c}^{+3}$ is least hydrated, i.e., least stable (not most stable).
$F$e ${}^{+2}$ contains 4 unpaired electrons whereas $M{n}^{+2}$ contains 5 unpaired electrons.