Question

The most stable complex among the following is:
A.${K_3}\left[ {Al\left( {{C_2}{O_4}} \right)} \right]$
B.$\left[ {Pt{{\left( {en} \right)}_2}} \right]Cl$
C.$\left[ {Ag{{\left( {N{H_3}} \right)}_2}} \right]Cl$
D.${K_2}\left[ {Ni\left( {EDTA} \right)} \right]$

Answer 1

Hint:This question gives the knowledge about complex ions and ligands. The cation to which one or more than one neutral molecules or ions are attached is known as the central ion whereas an ion or a molecule capable of donating a pair of electrons to the central atom through a donor atom is known as ligand.

Complete answer:
 Among all the complexes, ${K_2}\left[ {Ni\left( {EDTA} \right)} \right]$ is the most stable complex because it consists of a hexadentate ligand and as we know hexadentate ligand is a ligand which coordinate with central metal ion through six donor atoms are known as hexadentate ligands.
 In other complexes, ligands like $N{H_3}$ which is a monodentate ligand, ${C_2}{O_4}^{2 - }$ and $en$ which are bidentate ligands are present. These ligands form less stable complexes due to chelate effect.

Therefore, option $D$ is the correct option.

Note:
The cation to which one or more than one neutral molecules or ions are attached is known as the central ion whereas an ion or a molecule capable of donating a pair of electrons to the central atom through a donor atom is known as ligand.
Types of ligands:
 Monodentate ligands: Ligands which coordinate with central metal ions through one donor atoms are known as monodentate ligands. Example:$N{H_3}$ , $C{l^ - }$etc.
Bidentate ligands: Ligands which coordinate with central metal ion through two donor atoms are known as bidentate ligands. Example: ethylenediamine, ${C_2}{O_4}^{2 - }$(oxalate ion) etc.
Tridentate ligand: Ligands which coordinate with central metal ions through three donor atoms are known as tridentate ligands. Example: diethyl triamine.
Hexadentate ligands: Ligands which coordinate with central metal ions through six donor atoms are known as hexadentate ligands. Example: \[\;EDTA\] (ethylenediamine tetraacetate).