Which one of the following molecules has maximum dipole moment?

🧠 Dipole moment depends on both the magnitude of individual bond dipoles and their vector sum. Symmetric molecules cancel out to zero; asymmetric molecules add up. The lone pair on N also contributes to the molecular dipole.

• $\ce{CH4}$: tetrahedral, all C–H bonds equal → net $\mu = 0$
• $\ce{PF5}$: trigonal bipyramidal, symmetric → net $\mu = 0$
• $\ce{NF3}$: pyramidal. N–F bond dipoles point toward F (F is more electronegative). The lone pair moment on N points opposite to the N–F moments → partial cancellation → small $\mu$ ≈ 0.23 D
• $\ce{NH3}$: pyramidal. N–H bond dipoles point toward N (N is more electronegative than H). The lone pair moment on N points in the same direction as the bond moments → reinforcement → large $\mu$ ≈ 1.46 D

$\boxed{\text{Answer: (d) } \ce{NH3}}$