Which of the following compounds has the highest dipole moment?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Acetophenone
Oxygen is more electronegative than carbon, so the C=O bond is strongly polarised. Acetophenone, \( \ce{C6H5COCH3} \), is a ketone with this polar carbonyl group and has a substantial dipole moment.
Why the other options are incorrect
Option (1) trans-But-2-ene — Incorrect. A hydrocarbon with its two \( \ce{CH3} \) groups on opposite sides of the double bond; the bond dipoles cancel, so its dipole moment is zero.
Option (2) 1,3-Dimethylbenzene — Incorrect. A hydrocarbon with only C–C and C–H bonds; it is nearly non-polar.
Option (4) Ethoxyethane — Incorrect. An ether is polar, but carbonyl compounds are more polar than ethers.
NCERT (2026-27 edition):
8.1.2 Structure of the Carbonyl Group – “The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. … Carbonyl compounds have substantial dipole moments and are polar than ethers.”