JEE Main · 2026 · 23 Jan 2026 · Shift 1 · Hydrocarbons

But-2-yne takes up one mole of hydrogen over palladium on carbon by syn addition to give cis-but-2-ene (X), while dissolving-metal reduction with sodium in liquid ammonia proceeds by anti addition to give trans-but-2-ene (Y); the two are cis-trans stereoisomers, so statement A is true. The cis isomer carries its methyl groups on the same side and has a small but non-zero dipole moment, whereas only the trans isomer is non-polar, so the claim that X has zero dipole moment is wrong. Being more polar, the cis isomer has the higher boiling point, so statement C is true. Reductive ozonolysis of either but-2-ene cleaves the same internal double bond to give acetaldehyde from both, so the claim that they give different products is wrong. The incorrect statements are B and D.