A) \[{{V}^{2+}}<C{{r}^{2+}}<M{{n}^{2+}}<F{{e}^{2+}}:\] paramagnetic behavior
B) \[N{{i}^{2+}}<C{{o}^{2+}}<F{{e}^{2+}}<M{{n}^{2+}}:\] ionic size
C) \[C{{o}^{3+}}<F{{e}^{3+}}<C{{r}^{3+}}<S{{c}^{3+}}:\] stability in aqueous solution
D) \[Sc<Ti<Cr<Mn:\] number of oxidation states
Correct Answer: A
Solution :
[a] [a] \[V=3{{d}^{3}}4{{s}^{2}};\] \[{{V}^{2+}}=3{{d}^{3}}=3\] unpaired electrons \[Cr=3{{d}^{5}}4{{s}^{1}};\] \[C{{r}^{2+}}=3{{d}^{4}}=4\] unpaired electrons \[Mn=3{{d}^{5}}4{{s}^{2}};\] \[M{{n}^{2+}}=3{{d}^{5}}=5\] unpaired electrons \[Fe=3{{d}^{6}}4{{s}^{2}};\] \[F{{e}^{2+}}=3{{d}^{6}}=4\] unpaired electrons Hence the correct order of paramagnetic behaviour \[{{V}^{2+}}<C{{r}^{2+}}=F{{e}^{2+}}<M{{n}^{2+}}\] [b] For the same oxidation state, the ionic radii generally decreases as the atomic number increases in a particular transition series. Hence the order is \[M{{n}^{2+}}>F{{e}^{2+}}>C{{o}^{2+}}>N{{i}^{2+}}\] [c] In solution, the stability of the compound depends upon electrode potentials, SEP of the transitions metal ions are given as \[C{{o}^{3+}}/Co=+1.97,\]\[F{{e}^{3+}}/Fe=+0.77;\] \[C{{r}^{3+}}/C{{r}^{2+}}=-0.41,\]\[S{{c}^{3+}}\] is highly stable as it does not show + 2 0. S. [d] \[Sc-(+2),\]\[(+3)\] \[Ti-(+2),\]\[(+3),\]\[(+4)\] \[Cr-(+1),\]\[(+2),\]\[(+3),\]\[(+4),\]\[(+5),\]\[(+6)\] \[Mn-(+2),\]\[(+3),\]\[(+4),\]\[(+5),\]\[(+6),\]\[(+7)\] i.e. \[Sc<Ti<Cr<Mn\]
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