Question

Choose incorrect stability order :

• A. $\left[Cu\right(N{H}_3{)}_4{]}^{2+}<Cu(en{)}_2{]}^{2+}<[Cu\left(trien\right){]}^{2+}$
• B. $\left[Fe\right(H_{2}O{)}_6{]}^{3+}<\left[Fe\right(N{O}_2{)}_6{]}^{3+}<\left[Fe\right(N{H}_3{)}_6{]}^{3+}$
• C. $\left[Co\right(H_{2}O{)}_6{]}^{3+}<\left[Rh\right(H_{2}O{)}_6{]}^{3+}<\left[Ir\right(H_{2}O{)}_6{]}^{3+}$
• D. $\left[Cr\right(N{H}_3{)}_6{]}^{1+}<\left[Cr\right(N{H}_3{)}_6{]}^{2+}<\left[Cr\right(N{H}_3{)}_6{]}^{3+}$

Answer 1

The correct option is B $\left[Fe\right(H_{2}O{)}_6{]}^{3+}<\left[Fe\right(N{O}_2{)}_6{]}^{3+}<\left[Fe\right(N{H}_3{)}_6{]}^{3+}$

(A) The increasing stability order is $\left[Cu\right(N{H}_3{)}_4{]}^{2+}<Cu(en{)}_2{]}^{2+}<[Cu\left(trien\right){]}^{2+}$.
This is same as the increasing order for the density of the ligand.
Ammonia, ethylene diamine and triethylene tetramine are mono, bi and tetradentate ligands respectively.
Thus option A is correct.
(B) The increasing stability order is $\left[Fe\right(H_{2}O{)}_6{]}^{3+}<\left[Fe\right(N{H}_3{)}_6{]}^{3+}<\left[Fe\right(N{O}_2{)}_6{]}^{3+}$.
This is because nitro is stronger ligand than ammonia.
Thus option B is incorrect.
(C) The increasing stability order is $\left[Co\right(H_{2}O{)}_6{]}^{3+}<\left[Rh\right(H_{2}O{)}_6{]}^{3+}<\left[Ir\right(H_{2}O{)}_6{]}^{3+}$.
This is because the value of the effective nuclear charge $Z_{eff}$ increases from $C{o}^{3+}toI{r}^{3+}$.
Thus option C is correct.
(D) The correct stability order is $\left[Cr\right(N{H}_3{)}_6{]}^{1+}<\left[Cr\right(N{H}_3{)}_6{]}^{2+}<\left[Cr\right(N{H}_3{)}_6{]}^{3+}$.
This is because the oxidation state of chromium increases from $+1to+3.$
Thus option D is correct.