Question

Q. 17 the trans-alkenes are formed by the reduction of alkynes with :

Answer 1

Trans - alkane are formed by the reduction of alkynes with the use of sodium dissolved in a ammonia solvent.

in this case, A sodium radical donates an electron to one of p bond in a carbon - carbon triple bond. this forms anion, which can be protonated by hydrogen in an ammonia solvent. this prompts another sodium radical to donate an electron of 2nd p- bond in carbon - carbon triple bond.
soon after this , anion is protonated by hydrogen in an ammonia solvent to form $\textbf{Trans-alkene}$

mechanism of the given reaction is shown in attachment. here you can briefly understand how, hydrogenation of alkynes into Trans-alkene.