In allene (C₃H₄), the type(s) of hybridization of the carbon atoms is (are) :

${\mathrm{H}}_2\underset{{\mathrm{sp}}^2}{\mathrm{C}}=\underset{\mathrm{sp}}{\mathrm{C}}=\underset{{\mathrm{sp}}^2}{\mathrm{C}}{\mathrm{H}}_2$

In allene, The central carbon is attached to other carbons by two sigma and two pi bonds so it's hybridization will be sp.

The terminal carbon is attached to other carbon and hydrogen by 3 sigma and 1 pi bonds and hence, it's hybridization will be sp².