Based on the wavelength of maximum absorption of the cobalt complexes, arrange the following ligands in a spectrochemical series from weakest-field to strongest-field ligand. 

(a) Cl^- < NCS^- < H₂O < NH₃ 

(b) Cl^- < NCS^- < H₂O < NH₃ 

(c) H₂O < Cl^- < NH₃ < NCS^-

(d) Cl^- < H₂O < NCS^- < NH₃

Video transcript

All right. Hi everyone. So this question says to consider the following chromium complex ions and their wavelength of maximum absorptions list the ligands in a spectra chemical series from strongest field to weakest field ligand. So here in this case, we have four answer choices. Each arranging the ligands, chloride, water cyanide and ammonia in different orders. So let's begin by talking about delta, right? We're called delta is the crystal field splitting energy. In other words, delta represents the energy required to achieve an electronic transition from the lower energy the orbitals to the higher energy the orbital. Now this splitting energy is heavily influenced by the nature of the leg in itself, right? Because strong field Liggins will subsequently have a high value or delta where is weaker field legends will subsequently have a lower value for delta. And energy is also proportional to the wavelength of maximum absorption because we call it E which is energy is equal to H multiplied by C divided by lambda. Now H is planks constant C is the speed of light and lambda is the wavelength of light absorbed. Now, as you can see here, energy and wavelength are inversely proportional to each other, which means that as one increases the other must decrease. In other words, the higher the energy value, the shorter the wavelength of maximal absorption must be. So if the strong field ligands have a high delta value for the splitting energy, that means they have to have a shorter wavelength of maximum absorption. So in this case, if I scroll down and open some more space for myself, the goal here is to arrange our legends from strongest field to weakest field. So that means I'm going to start with my shortest wavelength to my highest one because that will correspond to strongest field to weakest field, right? And of the wavelengths that are listed in the table given on the screen here, the shortest one is 376 nanometers which corresponds to the complex ion involving cyanide. The cyanide has the shortest wavelength followed by ammonia at 465 nanometers. Next would be water with a wavelength of 575 nanometers. And finally, I have chloride at 769 nanometers. So be cyanide has the shortest wavelength of maximum absorption. It is the stronger field like followed by ammonia, water. And then lastly chloride being the weaker field like it. So our answer is going to be option B in the multiple choice. And with that being said, thank you so very much for watching. And I hope we found this helpful