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NEET levelSingle correct optionDifficulty 1 of 3hc021

Which reagent converts an alkyne into a cis-alkene?

A $Na$ in liquid $NH X_{3}$
B $H X_{2}$ over Lindlar's catalyst
C $LiAlH X_{4}$
D $H X_{2}$ over Ni at high temperature

Answer: B

Lindlar's catalyst (poisoned

Pd

) delivers two hydrogens to the same face of the triple bond, giving the cis-alkene.

Na / NH X_{3} (l)

gives the trans-alkene, and Ni/

H X_{2}

goes on to the alkane.

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