Explanation:

Dipole Moment:

- Dipole moment is a measure of the separation of positive and negative charges in a molecule.
- It is a vector quantity, with direction from the positive to the negative end of the molecule.

Trans-2-butenal:

- Trans-2-butenal has a double bond between the second and third carbon atoms, creating a more polarized molecule.
- The oxygen atom in trans-2-butenal is more electronegative than carbon, resulting in a larger dipole moment.
- The dipole moment of trans-2-butenal is higher due to the presence of the double bond and the oxygen atom, leading to a more polar molecule.

Butanal:

- Butanal does not have a double bond or an oxygen atom attached to the carbon chain.
- The absence of these more electronegative atoms results in a lower dipole moment compared to trans-2-butenal.
- The dipole moment of butanal is lower as the molecule is less polar overall.

Conclusion:

- In conclusion, trans-2-butenal has a greater dipole moment compared to butanal due to the presence of a double bond and an oxygen atom, making it a more polar molecule.

Ans is butanal bcz trans effect cancells dipole momment..