How many isomers are there with the formula c3h4? include both structural and geometric isomers?

There are three possible Isomers for Molecular Formula C₃H₄. Isomers are;

                                           1) Propyne

                                           2) Propa-1,2-diene

                                           3) Cyclopropene

Structures of all three isomers are given below.

There are no geometrical isomers for given molecular formula because geometrical isomers are formed in compounds containing double bond with at least two bulky groups at both sp² hybridized carbons. In given isomers, propyne does not contain any double bond, Propa-1,2-diene is symmetrical in nature while cyclopropene is a 3-membered ring. And for cycloalkenes there must be other groups attached to ring other than Hydrogen atom, hence cyclopropene does not contain any other group, so it can not show geometrical isomerism.

Ido not understand.