In the following sequence of reactions the maximum number of atoms present in molecule ' C ' in one plane is \ \ \ \. A →[ Cu tube ] Red hot B →[…

In the following sequence of reactions the maximum number of atoms present in molecule ' $\displaystyle C$ ' in one plane is \_\_\_\_. $$\mathrm{A} \xrightarrow[\text { Cu tube }]{\text { Red hot }} \mathrm{B} \xrightarrow[\text { Anhydrous } \mathrm{AlCl}_3]{\mathrm{CH}_3 \mathrm{Cl}(1 \text {.eq. })} \mathrm{C} $$ (A is a lowest molecular weight alkyne)