Q. What is Geometrical isomers?

Let us take one final example of Ma₂b₂cd where the following five isomers are possible as shown in Fig.

'When writing the geometrical isomers you must make sure that the relative positions of the ligands must be different in each configuration and it is not just a rotation of the molecule as a whole. The trick in writing these configurations is that if you fix the positing  of some ligands initially and rotate the other ligands, then write configuration with the changed positions of the ligands which were fixed earlier. For example, in the above case we have fixed the cis position for the two ligands 'a' and wrote all possible configurations I, II & III  Once that is over then we put the two 'a' ligands in trans-positions and again rotate their P ligands in all possible ways to get a different configuration. Finally. you must remember that  there is no formula available which can product the number of possible isomers for any  particular compound and hence, you have to try writing down all possible configurations in  each and every care (which of colour. require a lot' of patience and practice).