The existence of two different coloured complexes with the composition [Co(NH3)4Cl2] + is due to [CBSE AIPMT2010]

[Co(NH3)4Cl2]+ is an octahedral complex, in the form of [MA4B2] exhibiting two geometrical isomers (cis and trans). This gives two different colored complexes. Compounds that possess the same structural formula, but differ with respect to the positions of the identical groups in space are called cis-trans isomers and the phenomenon is known as Geometrical isomerism. Hence, the correct option is (c).