The order of polarity of NH₃, NF₃ and BF₃ is: · ABC26IN0461
Subject: Inorganic Chemistry · Chapter: Main Group Elements · Topic: Main Group Element – General · Exam: GATE 2005-2021 · Marks: 2 · Difficulty: Hard
The order of polarity of $\mathrm{NH}_{3}, \mathrm{NF}_{3}$ and $\mathrm{BF}_{3}$ is:
(a)$\mathrm{NH}_{3}<\mathrm{NF}_{3}<\mathrm{BF}_{3}$
(b)$\mathrm{BF}_{3}<\mathrm{NF}_{3}<\mathrm{NH}_{3}$
(c)$\mathrm{BF}_{3}<\mathrm{NH}_{3}<\mathrm{NF}_{3}$
(d)$\mathrm{NF}_{3}<\mathrm{BF}_{3}<\mathrm{NH}_{3}$
Answer
Answer: B ✓ checked by 4AB · confidence high
The source book printed A; on checking, B is correct — see the explanation.
Dipole moments NH3 1.47 D > NF3 0.23 D > BF3 0 D, i.e. increasing order BF3 < NF3 < NH3 = option (b); the earlier override to (a) reversed the order.
Explanation
NH₃ (μ ≈ 1.47 D): the N–H bond dipoles and the lone-pair moment point the same way and reinforce.
NF₃ (μ ≈ 0.23 D): the N–F bond dipoles point away from N and largely cancel the lone-pair moment.
BF₃: trigonal planar, bond dipoles cancel, μ = 0.
Order of polarity: BF₃ < NF₃ < NH₃ — option (b).
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