Which of the following is not used to distinguish ethene from ethane
D
Ammonical $$Cu_{2}Cl_{2}$$
Correct option is D. Ammonical $$Cu_{2}Cl_{2}$$
A. Addition Reaction of Alkenes with Halogens. ... Remember that the reactivity of halogen decreases in the group, so the excess reaction of alkanes with chlorine is faster with chlorine, which is the slowest of iodine compared to bromine.
B. Treatment of alkenes with bromine ($$Br_2$$) gives vicinal dibromides (1,2-dibromides). Notes: The bromines add to opposite faces of the double bond (“anti addition”). Sometimes the solvent is mentioned in this reaction – a common solvent is carbon tetrachloride ($$CCl_4$$).
C. Dihydroxylation of alkenes with cold, dilute $$KMnO_4$$ to give vicinal diols. Description: Treatment of alkenes with cold, dilute basic $$KMnO_4$$ leads to 1,2-diols (vicinal diols).
D. Ammonical $$Cu_2Cl_2$$ identification test for terminal alkynes and not for alkene and alkane. In this reaction, an terminal alkyne reacts with basic cupric chloride and on subsequent oxidation in air gives diyne. For example, ethyne couples with itself to produce but-1,3-yne (red brown ppt).
therefore on above explanation, we say that Option $$D$$ is a correct answer.