JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Chemical Bonding and Molecular Structure

The correct order of dipole moments for the given species is

Answer: (A)

Solution

Dipole moment analysis:

** $BF_{3}$ **: Trigonal planar, symmetrical → $μ_{n e t} = 0$
** $NH_{4}^{+}$ **: Tetrahedral, symmetrical → $μ_{n e t} = 0$
** $NF_{3}$ **: Pyramidal. The N-F bond dipoles point toward F (F is more electronegative), opposing the lone pair dipole on N. Net dipole ≈ $0.8 \times 1 0^{- 30}$ Cm (small)
** $NH_{3}$ **: Pyramidal. The N-H bond dipoles point toward N (N is more electronegative than H), reinforcing the lone pair dipole. Net dipole ≈ $4.90 \times 1 0^{- 30}$ Cm (large)

Order:

BF_{3} = NH_{4}^{+} < NF_{3} < NH_{3}

JEE Advanced · 2026 · 17 May 2026 · Paper 1 · Single correct option