Propyne and propene can be distinguished by

 Propene does not react with ammoniacal silver nitrate ${\mathrm{AgNO}}_3. \mathrm{Propyne}, \mathrm{on} \mathrm{the} \mathrm{other} \mathrm{hand},\mathrm{produces} \mathrm{this} \mathrm{response}. \mathrm{Propyne} \mathrm{contain}s \mathrm{triple} \mathrm{bond} \mathrm{between} C_1 \mathrm{and} {\mathrm{C}}_2$. The alkyne is therefore terminal. The hydrogens in terminal alkynes are acidic. These hydrogens are removed, resulting in the formation of insoluble precipitates.

Therefore, the correct option is (D) ${\mathrm{AgNO}}_3\text{ solution in ammonia }$.