JEE Chemistry 2024 Question with Solution

Given: The molecules are $\mathrm{CCl_4}$, $\mathrm{CO_2}$, $\mathrm{CH_2{=}CH_2}$ and $\mathrm{CHCl_3}$.

Find: Which molecule is polar.

To determine polarity, examine molecular geometry and whether bond dipole moments cancel.

1. $\mathrm{CH_2{=}CH_2}$ is symmetric, so the bond dipole moments cancel and the molecule is nonpolar.
2. $\mathrm{CHCl_3}$ has a tetrahedral arrangement with three more electronegative chlorine atoms and one hydrogen atom. Because the arrangement is asymmetric, the bond dipoles do not cancel completely, so the molecule has a net dipole moment.
3. $\mathrm{CCl_4}$ contains polar $\mathrm{C{-}Cl}$ bonds, but its tetrahedral symmetry makes the dipoles cancel, so it is nonpolar.
4. $\mathrm{CO_2}$ is linear, and the two $\mathrm{C{=}O}$ bond dipoles are equal and opposite, so they cancel and the molecule is nonpolar.

Therefore, the only polar molecule is $\mathrm{CHCl_3}$. The correct option is D.

The solution shows option B, but the worked explanation clearly concludes $\mathrm{CHCl_3}$, which corresponds to option D in the given list.

Given: Four molecules are listed.

Find: The polar molecule.

Use a symmetry check. If identical bond dipoles are arranged symmetrically, they cancel.

• $\mathrm{CCl_4}$: symmetric tetrahedral, nonpolar.
• $\mathrm{CO_2}$: symmetric linear, nonpolar.
• $\mathrm{CH_2{=}CH_2}$: symmetric molecule, nonpolar.
• $\mathrm{CHCl_3}$: not symmetrically substituted, so the dipoles do not cancel.

Hence, $\mathrm{CHCl_3}$ is polar, so the correct option is D.