Correct Answer: D
Explanation:
In organic compounds triple covalent bonds are, in general, less stable than double bonds. Double bonds are less stable than single bonds. In a triple bond and in the double bond there will be six, respectively four electrons trying to occupy a small space, in between the two carbon atoms of ethyne and ethene, while they will repel one another (same charge particles). So double and triple bonds will practically un-stable.
The single covalent bond is the most stable, thus the least reactive, because the 2 electrons are more comfy in their orbits.