Concept:Ethyne is a terminal alkyne with an acidic hydrogen, so it forms a characteristic precipitate with ammoniacal silver trioxonitrate(V), whereas ethene does not.
Explanation:Take two test tubes containing ethene and ethyne gas separately.
Add a few drops of ammoniacal silver trioxonitrate(V) solution to each test tube.
Ethene gives no visible change because it is an alkene and has no terminal acidic hydrogen atom.
Ethyne reacts with the reagent and gives a white precipitate of silver acetylide.
The reaction is:
C2H2+2AgNO3+2NH4OH→Ag2C2↓+2NH4NO3+2H2OOnly ethyne produces this white precipitate, so the two gases are easily distinguished.
Bromine water cannot distinguish them because both ethene and ethyne decolourise bromine water.
Answer:A. ammoniacal silver trioxonitrate (V) solution