Ethene and ethyne can be distinguished using 

Two carbons doubly bonded are known as alkene and two carbons triply bonded are known as alkyne. Ethene is represented as ${\mathrm{H}}_2\mathrm{C}={\mathrm{CH}}_2$ and ethyne as$\mathrm{HC}\equiv \mathrm{CH}$.

Acetylene (terminal alkyne) when reacted with ${\mathrm{NH}}_4\mathrm{OH}$ and ${\mathrm{AgNO}}_3$ (Tollen's reagent) gives a black precipitate of ${\mathrm{Ag}}^{+}$. 

Whereas ethene doesn’t respond to Tollen’s test because aldehydes and alkynes only show Tollen’s test. Hence, ethene and ethyne can be distinguished by Tollen’s reagent.

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