Question

In allene $(C_3H_4)$ the type(s) of hybridisation of the carbon atoms, is (are)

• A. $sp \, and \, sp^3$
• B. $sp \, and \, sp^2$
• C. $only \, sp^3$
• D. $sp^2 \, and \, sp^3$

Answer 1

Answer: (B)

$sp \, and \, sp^2$

Answer 2

Allene is the name given to propdiene, $_{ \, \, \, \, \, \, \, \, Allene}^{H_2C = C = CH_2}$

Hybridisation of an atom is determined by determining the number of hybrid orbitals at that atom which is equal to the number of sigma $(s)$ bonds plus number of lone pairs at the concerned atom.
Pi$(p)$ bonds are not formed by hybrid orbitals, therefore, not counted for hybridisation.
Here, the terminal carbons have only three sigma bonds associated with them, therefore, hybridisation of terminal carbons is $sp^3$. The central carbon has only two sigma bonds associated, hence hybridisation at central carbon is sp.

So, the correct answer is (B): sp and sp 2