Transition and InnerTransition Elements - Result Question 23
####24. Which of the following arrangements does not represent the correct order of the property stated against it? (2013 Main)
(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
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Solution:
- (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)
$$ \begin{aligned} Co^{3+} / Co^{2+} & =1.97 ; \ Fe^{3+} / Fe^{2+} & =0.77 ; \ Cr^{3+} / Cr^{2+} & =-0.41 \end{aligned} $$
$Sc^{3+}$ 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.
