In the following sequence of reactions the maximum number of atoms possible in molecule ‘C’ in one plane is

$\mathrm{A}\underset{\text{Cu tube}}{\overset{\text{Red hot}}{\to }}\mathrm{B}\underset{{\text{Anhydrous AlCl}}_3}{\overset{{\mathrm{CH}}_3\mathrm{Cl}\left(1\mathrm{eq}.\right)}{\to }}\mathrm{C}$

(A is a lowest molecular weight alkyne).