A central metal ion form four complexs with ligands l1, l2, l3, l4 the order of ligand strength is l1>l2>l4>l3, then the colour of complex M(l4) 6 is blue then

The question is based on colour wheel (VBGYOR) in coordination compounds

Ligand strength is inversely proportional to wavelength  .and in Vibgyor from left to right wavelength increase frequency decrease implies red has highest wavelength 

Concept of colour wheel is like ligand which is strongest means have least wavelength,, let violet colour will transmit colour opposite to violet in colour wheel i.e. yellow(u can refer on net as here not possible to draw) . 

L1 strongest means less wavelength color absorbed i.e.green and emit colour opposite to it in colour wheel I.e.red and similarly for others 

 

Note colour we see is the cour that is emitted not the absorbed one 

So according to me answer should be last option

Hope it helps

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