Question

Which of the following compounds is not coloured yellow?
A.$Z{n_2}[Fe{\left( {CN} \right)_6}]$
B.$BaCr{O_4}$
C.${K_3}[Co{\left( {N{O_2}} \right)_6}]$
D.${\left( {N{H_4}} \right)_3}[As{\left( {M{o_3}{O_{10}}} \right)_4}]$

Answer 1

As we know that a coordination complex contains the central metal atom which is usually metallic and this center is known as coordination center. This metal is surrounded with a group of ions or molecules and these are known as complexing agents or ligands. All the coordination complexes have different physical and chemical properties like colour, solubility, catalytic activity, oxidation and reduction activity, etc.

Complete answer:
Among the given coordination complexes,$Z{n_2}[Fe{\left( {CN} \right)_6}]$, (zinc cyanoferrate) is not yellow in colour. And the colour of $Z{n_2}[Fe{\left( {CN} \right)_6}]$ is bluish white. When the potassium ferrocyanide is reacting with zinc ions there is a formation of bluish white precipitate of zinc cyanoferrate.
Generally the colour of the coordination complex can be explained on the basis of crystal field theory. And the coloured compounds can be used in textile industries for the preparation of pigments for dye. While the formation of coordination complex, the electrons present in the d – orbital may split into higher energy orbitals and the lower energy orbitals. The ions with noble gas electronic configuration does not contain any unpaired electrons. Therefore, the complex becomes colorless. And here, $Z{n_2}[Fe{\left( {CN} \right)_6}]$ is not yellow in colour. Hence, option (a) is correct.
The color of $BaCr{O_4}$, (barium tetroxochromate) is yellow and it is a sand like powder. Hence, option (b) is incorrect.
The ${K_3}[Co{\left( {N{O_2}} \right)_6}]$ complex has a yellow color. Hence, option (c) is incorrect.
The colour of${\left( {N{H_4}} \right)_3}[As{\left( {M{o_3}{O_{10}}} \right)_4}]$is yellow in nature. Hence, the option (d) is incorrect.

Hence, option (a) is correct.

Note:
We need to know that the coordination complex is formed by the reaction of transition metal with ligands. And all the complexes have different properties and different colors. If the compounds have noble gas configuration, the solution should be colorless. If the transition metal contains more unpaired electrons, the complex will show colors in both solution state and solid state. The colour of the complex appears from the transition of electrons between the energy levels.