Question

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

• A. $V ^{2+} < Cr^{2+} < Mn^{2+} < Fe^{2+}$: paramagnetic behaviour
• B. $Ni^{2+} < Co^{2+} < Fe^{2+} < Mn^{2+}$ : ionic size
• C. $Co^{3+} < Fe^{3+} < Cr^{3+} < Sc^{3+}$ : stability in aqueous solution
• D. $Sc < Ti < Cr < Mn$ . number of oxidation states

Answer 1

Answer: (A)

(a) $V^{2+} = 3$ unpaired electrons
$Cr^{2+} = 4$ unpaired electrons
$Mn^{2+} = 5$ unpaired electrons
$Fe^{2+} = 4$ unpaired electrons
Hence, the order of paramagnetic behaviour should be
$ V^{2+} < Cr ^{2+} = Fe^{2+} < Mn^{2 +}$
(b) Ionic size decreases from left to right in the same period
(c) (As per data from NCERT)
$ Co^{3+} / Co^{2+} = 1.97;$
$ Fe^{3+} / Fe^{2+} = 0.77; $
$ Cr^{3+} / Cr^{2+} =-0.41;$
$Sc^{3+}$ is highly stable (It does not show $+ 2$).
(d) The oxidation states increases as we go from group $3$ to group $7$ in the same period.