Owing to the fact that allene is not a planar molecule, the hydrogen atoms in the molecule do not lie on the same plane.
A planar molecule refers to those molecules that lie on same plane. This means that the atoms in the molecules are all arranged along the same plane.
Now we know that the molecule allene is not a planar molecule. Owing to the fact that allene is not a planar molecule, the hydrogen atoms in the molecule do not lie on the same plane. All the carbon atoms present are sp2 hybridized.
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