Question

are unsaturated very reactive?

Answer 1

yes due to their unsaturation they would like to react and get converted to saturated once:)
for example
ethyne is more recative then ethene followed by ethane:)
bcoz the unsaturation is high in case of ethyne then ethene :) further u go the ethene is more unsaturated than ethane :) so the tread
ethyne>ethene>ethane

Answer 2

another important thing about unsaturation they have loosely held pie electron which can share or form bonds with other very easily unlike the sigma bond:)