Propyne because of the presence of acidic H-atom, reacts with ammoniacal AgNO3 and gives grey/white silver propynilide. Propene, on the other hand, does not have any acidic H-atom, so it does not react with ammoniacal AgNO3. Hence, these two are separated by this reagent. CH3C≡≡CH+AgNO3+NH4‌OH⟶
CH3C≡CAg
silver‌propynilide
↓+NH4NO3+H2O CH3‌CH=CH2+AgNO3+NH4‌OH ⟶ No reaction