Chemistry Chemical Bonding NUMS 2019
PMDC Verified Question 75 of 102
Which of the following molecule has zero dipole moment?
A
\( \text{PCl}_3 \)
B
\( \text{BF}_3 \)
C
\( \text{NH}_3 \)
D
\( \text{H}_2\text{O} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{BF}_3 \)
Concept:

Dipole moments cancel out entirely in highly symmetrical molecules lacking lone pairs on the central atom.

Formula:

$$ \text{Net Dipole } (\mu) = 0 $$

Solution:

  • As established, Boron trifluoride (\( \text{BF}_3 \)) has perfectly symmetrical trigonal planar geometry.


  • Because all B-F bonds are identical and spaced equally at 120°, their individual dipole vectors cancel completely.


Why other options are incorrect:

  • Option A, Option C, Option D: All possess lone pairs on the central atom, creating asymmetric shapes (pyramidal and bent) that prevent dipole cancellation.

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