Covalent molecules formed by heteroatoms bound to have some ionic character. The ionic character is due to shifting of the electron pair towards A or B in the molecule AB. Hence, atoms acquire small and equal charge but opposite in sign. Such a bond which has some ionic character is described as polar covalent bond. Polar covalent molecules can exhibit dipole moment. Dipole moment is equal to the product of charge separation, q and the bond length, d for the bond. The unit of dipole moment is Debye. One Debye is equal to `10^(-18)` esu cm.
Dipole moment is a vector quantity. It has both magnitude and direction. Hence, dipole moment of molecules depends upon the relative orientation of the bond dipoles, but not on the polarity of bonds alone. A symmetrical structure shows zero dipole moment. Thus, dipole moments help to predict the geometry of the molecules. Dipole moment values can be used to distinguish between cis-and traps-isomers, ortho-, meta-and para-forms of a substance, etc. The percentage of ionic character of a bond can be calculated by the application of the following formula :
`% " ionic character " = ("Experimental value of dipole moment ")/("Theoretical value of dipole moment ") xx 100`
The dipole moment of `NF_(3)` is very much less than that of `NH_(3)` because :

Options

A. Number of lone pairs in `NF_(3)` is much less greater than in `NH_(3)`
B. unshared electron pair is not present in NF as in `NH_(3)`
C. both have different shapes
D. of different directions of moments of N-H and N-F bonds

Answer

C