JEE Main 2023 — Chemistry Inorganic Chemistry

2023mcqeasy

The Lewis acid character of boron tri halides follows the order:

Official previous-year question

Held on 31 Jan 2023 · Verified 6 Jul 2026.

Options

A
${\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}$
B
${\mathrm{Bl}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}$
C
${\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}$
D
${\mathrm{BF}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}$

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Solution

The strength of the acidic character of boron trihalides depends upon $\pi -\pi$ back bonding. In boron trihalides, $\pi -\pi$ -back bonding occurs due to empty orbital of boron and filled orbitals of halogens.

JEE Main 2023 Chemistry, p Block Elements (Group 13 and 14) — solution figure

The $\pi -\pi$ back bonding is shown maximum by ${\mathrm{BF}}_{3}$ , as the size of B and F are small and comparatively same. Due to this effect tendency of accepting lone-pair of electrons of boron decreases as the size of halogen increases. The order of size of halogens are $F<\mathrm{Cl}<\mathrm{Br}<I$ . Thus, acidic nature is in order ${\mathrm{BF}}_{3}<{\mathrm{BCl}}_{3}<{\mathrm{BBr}}_{3}<{\mathrm{Bl}}_{3}$ .

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Options

${\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}$

${\mathrm{Bl}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}$

${\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BF}}_{3}$

${\mathrm{BF}}_{3}>{\mathrm{BCl}}_{3}>{\mathrm{BBr}}_{3}>{\mathrm{Bl}}_{3}$

Solution

JEE Main 2023 Chemistry, p Block Elements (Group 13 and 14) — solution figure

JEE Main 2023 — Chemistry Inorganic Chemistry

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JEE Main 2023 — Chemistry Inorganic Chemistry

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