A gas formed by the action of alcoholic KOH on ethyl iodide, decolorizes alkaline KMnO4 solution. The gas is
C2H4
We know that,
Alkyl halide o reaction with alcoholic KOH or NaOH gives alkene.
R−CH2−CH2−X+KOH(alc)⟶R−CH=CH2+KX+H2O
And
Hydroxylation using KMnO4:1% cold alkaline KMnO4 solution (Baeyer's reagent) or dil.KMnO4 gives glycol
Note.
(a) It is an unsaturation test because the pink colour of solution disappears.
(b) It is a example of Syn-addition.
Therefore,
CH3CH2l+KOH(alc)⟶CH2=CH2+Kl+H2O