Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYMedium

Which of the following set of molecules will have zero dipole moment?

Boron trifluoride, hydrogen fluoride, carbon dioxide, 1,3-dichlorobenzene

Nitrogen trifluoride, beryllium difluoride, water, 1,3-dichlorobenzene

Boron trifluoride, beryllium difluoride, carbon dioxide, 1,4-dichlorobenzene

Ammonia, beryllium difluoride, water, 1,4-dichlorobenzene

Condition for Zero Dipole Moment: A molecule has a zero dipole moment ( $\mu = 0$ ) if it is highly symmetrical such that the individual bond dipoles cancel out vectorially.
Analyze the Correct Set (Option C):

Boron trifluoride ( $BF_3$ ): Has a trigonal planar geometry ( $sp^2$ ). The three B-F bond dipoles are at $120^\circ$ to each other and cancel out completely.
Beryllium difluoride ( $BeF_2$ ): Has a linear geometry ( $sp$ ). The two Be-F bond dipoles are at $180^\circ$ and cancel each other.
Carbon dioxide ( $CO_2$ ): Has a linear geometry ( $sp$ ). The two C=O bond dipoles are equal and opposite, cancelling out.
1,4-dichlorobenzene ( $p$ -dichlorobenzene): This is the para-isomer. The two C-Cl bonds are on opposite sides of the benzene ring ( $180^\circ$ ). Due to the symmetry of the molecule, the bond moments cancel out .

Polar Molecules ( $\mu \neq 0$ ): Hydrogen fluoride ( $HF$ , diatomic polar), Water ( $H_2O$ , bent, lone pairs), Ammonia ( $NH_3$ , pyramidal, lone pair), Nitrogen trifluoride ( $NF_3$ , pyramidal, lone pair), and 1,3-dichlorobenzene (meta-isomer, angle $120^\circ$ , vectors do not cancel) .

Conclusion: Only the set in Option C consists entirely of non-polar molecules.

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