What is meant by hybridisation? The compound $CH_2 = C = CH_2$ contains $sp$ and $sp^2$ hybridised carbon atoms. Will it be a planar molecule?

(N/A) Hybridisation is the phenomenon of mixing of atomic orbitals of the same atom having comparable energies to form an equal number of new hybrid orbitals with similar energies and shapes.
In the allene molecule $(CH_2=C=CH_2)$:
- The terminal carbon atoms ($C_1$ and $C_3$) are bonded to two hydrogen atoms and one carbon atom via $\sigma$-bonds. They are $sp^2$ hybridised.
- The central carbon atom $(C_2)$ is bonded to two carbon atoms via $\sigma$-bonds. It is $sp$ hybridised.
Regarding planarity:
- The $C_1$ carbon and its attached hydrogen atoms lie in one plane.
- The $C_3$ carbon and its attached hydrogen atoms lie in a plane perpendicular to the plane of the $C_1$ hydrogen atoms.
- This is because the two $\pi$-bonds formed by the central $sp$-hybridised carbon involve different sets of $p$-orbitals ($2p_y$ and $2p_z$),which are mutually perpendicular.
- Therefore,the allene molecule is non-planar.