Q.Arrange following hydrocarbons in the increasing order of acidic character: propane, propyne, propene.

A terminal alkyne's C-H hydrogen sits on an sp-hybridised carbon, whose hybrid orbital has 50% s-character; because electrons in an s-orbital sit especially close to (and are held especially tightly by) the nucleus, this makes an sp carbon more electronegative than the sp2 carbon of an alkene or the sp3 carbon of an alkane, and the attached hydrogen becomes appreciably acidic -- removable as a proton by a sufficiently strong base such as lithium amide, which converts a terminal alkyne into its lithium acetylide plus ammonia gas. This gives the relative acidity order ethyne > ethene > ethane, since alkenes and alkanes simply lack any comparably acidic hydrogen and do not react …