Question

Out of NH3 & BF3 Which is polar & Why?

Answer 1

NH3 is polar becuz of the presence of lone pairs on N atom,but in the case of BF3 there is no lone pair on B and thus no net dipole moment.[Although 3 F atoms are attached].

Answer 2

NF3 is trigonal pyramidal in shape. ... Although the bonds in BF3 are morepolar, with a difference of 2.0, the trigonal planar shape is symmetrical, and the electronegativity differences cancel out. Because BF3 doesn't meet both requirements of polar molecules, it is considered non-polar.