Assertion (A): BF3 has zero dipole moment. Reason (R): Each B–F bond is polar because fluorine is more electronegative than boron.
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BF3 is trigonal planar, so the three equal B–F bond dipoles cancel and the resultant dipole moment is zero. The B–F bonds are indeed polar, but polarity of the bonds alone would give a dipole moment; it is the symmetrical shape, not the polarity, that explains the zero value.
- A.
The Reason explains why the bonds are polar, not why the molecule has zero dipole moment; the symmetry of the trigonal planar shape explains that.
- C.
The Reason is true: fluorine is more electronegative than boron, so B–F bonds are polar.
- D.
The Assertion is true: the bond dipoles in planar BF3 cancel to give zero dipole moment.
NCERT: Class 11 Chemistry, Chapter 4, 4.3