Question

Which of the following has maximum number of geometrical isomers ?

• A. $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Cl}}_2\right]$
• B. $\left[\mathrm{Ni}\left({\mathrm{C}}_2{\mathrm{O}}_4\right){\left(\mathrm{en}\right)}_2\right]$
• C. ${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$

Answer 1

The correct option is C

${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$

The explanation for the correct answer

(C) ${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$

1. ${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$ has maximum isomers structures as it can show linkage isomerism, geometrical isomerism and optical isomerism.
2. Linkage isomerism is due to the presence of an ambidient ligand $\mathrm{SCN}$ which can attack either from $-\mathrm{SCN}$ side or $-\mathrm{NCS}$ side.
3. Geometrical isomerism can exhibit Cis as well as trans isomers. When $\mathrm{SCN}$ on same side it is cis isomer and when on opposite site it is trans isomer.
4. In optical isomerism it may be D or L isomers.
5. Thus, ${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$has maximum number of isomers.

The explanation for the incorrect answers

(A) $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Cl}}_2\right]$

1. It can show only geometrical isomers that is cis and trans isomer.
2. When the $\mathrm{Cl}$ present on same side it show cis isomerism whereas if $\mathrm{Cl}$ is present on opposite side it shows trans isomerism.
3. Thus, it shows only two possible isomers.
4. Thus, it is an incorrect answer.

(B) $\left[\mathrm{Ni}\left({\mathrm{C}}_2{\mathrm{O}}_4\right){\left(\mathrm{en}\right)}_2\right]$

1. $\left[\mathrm{Ni}\left({\mathrm{C}}_2{\mathrm{O}}_4\right){\left(\mathrm{en}\right)}_2\right]$ shows optical isomerism.
2. It has two isomers D and L isomers,
3. Thus, it is also an incorrect answer.
   

Thus, ${\left[\mathrm{Cr}{\left(\mathrm{SCN}\right)}_2{\left({\mathrm{NH}}_3\right)}_4\right]}^{2+}$ has maximum number of isomers. Therefore, option C is correct.