Cumulene is an alkene hydrocarbon that has two or three double bonds. It is also known as allene. The simplest cumulene is butatriene. It is a rigid hydrocarbon due to the presence of double bonds.
Answer: The orbital that overlap are p/p overlap, s/sp2 overlap, sp/sp2 overlap and sp/sp orbital.
Since a radical is formed as part of the product it means it's a propagation step and not a termination step, at termination no free radical exist as product