Given below are two statements :
Statement (I) :
is more polar than
Statement (II) : Boiling point of
is lower than
but it is more polar than
.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 4 steps

In a cis isomer the two C–X dipoles add up; in the trans isomer they point opposite ways and cancel.

1. Statement I. Both molecules are cis, so the two C–X bond dipoles lie on the same side and add up. Cl is more electronegative than Br, so each C–Cl dipole is larger. That makes cis-ClCH=CHCl more polar than cis-BrCH=CHBr. Statement I is correct.
2. Trans has zero dipole. In trans-BrCH=CHBr the two C–Br dipoles are equal and point in opposite directions, so they cancel. Its net dipole moment is zero, so it is non-polar and cannot be more polar than the cis isomer.

   Molecule	C–X dipoles	Net dipole moment
   cis-ClCH=CHCl	add up, larger C–Cl dipoles	largest
   cis-BrCH=CHBr	add up, smaller C–Br dipoles	non-zero, smaller
   trans-BrCH=CHBr	equal and opposite, cancel	zero

3. Statement II. The first half is true: the trans isomer has a lower boiling point because it has no dipole–dipole attraction. The second half is false, because the trans isomer is less polar, not more. So Statement II is incorrect.
4. So. Statement I is correct and Statement II is incorrect, which is option (d).

The idea to keep. For a cis/trans pair with two identical groups, the trans isomer has zero dipole moment and the cis isomer is polar. Lower polarity means weaker dipole–dipole attraction, so the trans isomer boils lower.

Answer from the NTA final answer key. Solution by PrepWiser.