Question

The stability of complexes of $C{{u}^{2+}},\,\,N{{i}^{2+}},\,\,C{{o}^{2+}}$ and $F{{e}^{2+}}$ varies in the order:

• A. $C{{u}^{2+}}>N{{i}^{2+}}>C{{o}^{2+}}>F{{e}^{2+}}$
• B. $C{{u}^{2+}}>F{{e}^{2+}}>N{{i}^{2+}}>C{{o}^{2+}}$
• C. $N{{i}^{2+}}>C{{o}^{2+}}>F{{e}^{2+}}>C{{u}^{2+}}$
• D. $C{{u}^{2+}}>N{{i}^{2+}}>C{{o}^{2+}}>F{{e}^{2+}}$

Answer 1

Answer: (D)

$C{{u}^{2+}}>N{{i}^{2+}}>C{{o}^{2+}}>F{{e}^{2+}}$

Answer 2

When cations have some charge but number of $d-$ electrons are different then the stability (or CFSE) decrease with increase in the number of $d-$ electrons. Therefore, the correct order is: $F{{e}^{2+}}>C{{o}^{2+}}>N{{i}^{2+}}>C{{u}^{2+}}$