In the following sequence of reactions the maximum number of atoms present in molecule ‘C’ in one plane is _______ $\mathrm{A}\underset{\mathrm{Cu} \mathrm{tube}}{\overset{\mathrm{Redhot}}{\to }}\mathrm{B}\underset{\text{ Anhydrous }{\mathrm{Alcl}}_3}{\overset{{\mathrm{CH}}_3\mathrm{Cl}\left(\text{ 1 eq }\right)}{\to }}\mathrm{C}$