Question

# The correct increasing order of dipole moments for the given molecules is: (BF3,NF3 and NH3)BF3>NF3>NH3NF2>BF3>NH3NH3>NF3>BF3NH3>BF3>NF3

Solution

## The correct option is C NH3>NF3>BF3In NH3 and NF3, the central nitrogen has three σ bonds and one lone pair. Hence, both are sp3 hybridized and posses trigonal pyramidal shape. In BF3, the central boron has only three σ bonds and so it is sp2 hybridized and has trigonal planer shape. In BF3, the dipole moment vectors are arranged at 120∘. Therefore, the resultant of the two dipole moment vectors cancel out with the third dipole moment vector and hence BF3 is non polar in nautre. In NH3 and NF3, the dipole moment vectors do not cancel out each other. Hence, both the molecules are polar in nature. In NH3, the dipole moment vector of the bond and the lone pairs are in the same direction, while in NF3, the dipole moment vector of the lone pair and the bond pairs are opposite in direction. Hence, the dipole moment of  NH3 is larger than NF3.

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