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# Which of the following arrangement of molecules is correct on the basis of their dipole moments?

$(a)\;BF_3 > NF_3 > NH_3 \\ (b)\;NF_3 > BF_3 > NH_3 \\(c)\;NH_3 > BF_3 > NH_3 \\(d)\;NH_3 > NF_3 > BF_3$

Can you answer this question?

$BF_3$ is trigonal planar hence u=0
In $NF_3$ the lone pair moment opposes the dipole moments of $N.F$ bonds while in $NH_3$ the lone pair moment are added to the dipole moments of $N-H$ bonds.
So, $NH_3 > NF_3 > BF_3$
Hence d is the correct answer.
answered Apr 1, 2014 by