But-2-yne and hydrogen (one mole each) are separately treated with (i) $\mathrm{Pd} / \mathrm{C}$ and (ii) $\mathrm{Na} / \mathrm{liq}. \mathrm{NH}_{3}$ to give the products X and Y respectively. ![JEE Main 2026 Chemistry, Hydrocarbons — question figure](https://prepforbharat.s3.ap-south-1.amazonaws.com/exam/615f0e999476412f48314daf/Chemistry/images/Hydrocarbons/6983c1968bfdbb2435639697/question_1__q_6983c1968bfdbb2435639697__cdn-question-pool.getmarks.app__23S1_q_60_1__61c336e104_final_ppt_sync.png) Identify the incorrect statements. A. $X$ and $Y$ are stereoisomers. B. Dipole moment of X is zero. C. Boiling point of $X$ is higher than $Y$. D. X and Y react with $\mathrm{O}_{3} / \mathrm{Zn}+\mathrm{H}_{2} \mathrm{O}$ to give different products. Choose the correct answer from the options given below :

JEE Main 2026 — Chemistry Organic Chemistry

2026mcqmedium

But-2-yne and hydrogen (one mole each) are separately treated with (i) $\mathrm{Pd} / \mathrm{C}$ and (ii) $\mathrm{Na} / \mathrm{liq}. \mathrm{NH}_{3}$ to give the products X and Y respectively.

JEE Main 2026 Chemistry, Hydrocarbons — question figure

Identify the incorrect statements.

A. $X$ and $Y$ are stereoisomers.

B. Dipole moment of X is zero.

C. Boiling point of $X$ is higher than $Y$ .

D. X and Y react with $\mathrm{O}_{3} / \mathrm{Zn}+\mathrm{H}_{2} \mathrm{O}$ to give different products.

Choose the correct answer from the options given below :

Official previous-year question

Held on 23 Jan 2026 · Verified 6 Jul 2026.

Options

A
B and D Only
B
A and C Only
C
A and B Only
D
B and C Only

Did you get this right?

Solution

But-2-yne ( $CH_3-C\equiv C-CH_3$ ) undergoes partial hydrogenation.

Reaction with $Pd/C$ (Lindlar-like conditions for 1 mole $H_2$ ) gives cis-but-2-ene as product $X$ .

Reaction with $Na/liq. NH_3$ (Birch reduction) gives trans-but-2-ene as product $Y$ .

Statement A: $X$ (cis) and $Y$ (trans) are geometrical isomers, hence stereoisomers. This is correct.

Statement B: Cis-but-2-ene ( $X$ ) has a non-zero dipole moment ( $\mu \neq 0$ ) due to the additive nature of bond moments, while trans-but-2-ene ( $Y$ ) has zero dipole moment ( $\mu = 0$ ) due to symmetry. Thus, statement B is incorrect.

Statement C: Cis-isomers generally have higher boiling points than trans-isomers due to higher dipole-dipole interactions. So, B.P. of $X > Y$ . This is correct.

Statement D: Reductive ozonolysis ( $O_3/Zn, H_2O$ ) of both cis-but-2-ene and trans-but-2-ene yields the same product, ethanal ( $CH_3CHO$ ). Thus, statement D is incorrect.

The incorrect statements are B and D.

Your note

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Solution

But-2-yne ( $CH_3-C\equiv C-CH_3$ ) undergoes partial hydrogenation.

Reaction with $Pd/C$ (Lindlar-like conditions for 1 mole $H_2$ ) gives cis-but-2-ene as product $X$ .

Reaction with $Na/liq. NH_3$ (Birch reduction) gives trans-but-2-ene as product $Y$ .

Statement A: $X$ (cis) and $Y$ (trans) are geometrical isomers, hence stereoisomers. This is correct.

Statement C: Cis-isomers generally have higher boiling points than trans-isomers due to higher dipole-dipole interactions. So, B.P. of $X > Y$ . This is correct.

Statement D: Reductive ozonolysis ( $O_3/Zn, H_2O$ ) of both cis-but-2-ene and trans-but-2-ene yields the same product, ethanal ( $CH_3CHO$ ). Thus, statement D is incorrect.

The incorrect statements are B and D.

JEE Main 2026 — Chemistry Organic Chemistry

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Solution

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JEE Main 2026 — Chemistry Organic Chemistry

Options

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Solution

Your note

JEE Main Organic Chemistry in other years

More JEE Main Organic Chemistry questions

Other Chemistry topics for JEE Main

Physical Chemistry

Inorganic Chemistry

Keep practicing Organic Chemistry