Which of the following catalysts is used to convert $-\mathrm{C} \equiv \mathrm{C}-\mathrm{to}$
to form cis-alkene?

• A

  $\quad \mathrm{ZnCl}_2 / \mathrm{HCl}$
• Correct answer
  B

  $\quad \mathrm{Pd}-\mathrm{C}$ quinoline
• C

  Na / liquid $\mathrm{NH}_3$
• D

  $\mathrm{Na} / \mathrm{Hg}$ in $\mathrm{H}_2 \mathrm{O}$

Hence, the correct answer is option: 'B'.