74. Which of the following has highest dipole moment?
(A) NH₃                  (B) PH₃               (C) AsH₃                   (D) SbH₃.

75. Which of the following is least basic?
(A) NF₃                   (B) NH₃               (C) NCl₃                   (D) NI₃ 

74. NH₃ would have highest dipole moment. Nitrogen being more electronegative than P, As, Sb, leads to greater bond dipole moment and hence the total dipole moment is also Higher.

75. NI3 has highest dipole moment. As we move down the group, the electronegativity decreases. So, F is most electronegative and I is least electronegative. But Cl, Br and I are less electronegative than N and that is why the dipole moment will be towards the halogen. The N has one lone pair, so dipole moment will be in direction of lone pair. Both dipole moments will add up. In case of NF3, they will cancel. So, NF3 will have least dipole moment. Out of NBr3, NI3 and NCl3, the dipole moment will be maximum for NI3, as I is most electronegative.