JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Hydrocarbons

When acetylene is passed through a red-hot iron tube at $873\mathrm{K}$ it undergoes cyclic trimerisation, three molecules joining head to tail to give benzene, ${\mathrm{C}}_6{\mathrm{H}}_6$. In benzene every carbon lies in the planar aromatic ring and is bonded to three atoms, so all six ring carbons are $s{p}^2$ hybridised, and there is no carbon outside the ring. The number of $s{p}^2$ hybridised carbon atoms in the product is therefore six.