In the allene (h2c=c=ch2) molecule:
select one:
a. all the atoms lie in one plane.
b. the ð bonds are delocalised over all three c atoms.
c. the two h atoms on one c lie above and below the plane defined by the other ch2 group.
d. the nonbonding orbitals are full.
e. none of the other options

Option c

Explanation:

In the allene,

Central atom forms two sigma bond and two pi bond.

Hybridization of central atom = sp

Hybridization of two terminal C =

Allene is a nonplanar molecules. This is because of the planes of two groups which are twisted 90 ° to each other.

Therefore, the two H atoms on one C lie above and below the plane defined by the other group.