JEE Advanced 2022 Paper 2 Q11 Chemistry Inorganic Chemistry p-Block Elements (Groups 13-14) Medium

JEE Advanced 2022 Paper 2 · Q11 · p-Block Elements (Groups 13-14)

The compound(s) which react(s) with NH$_3$ to give boron nitride (BN) is(are)

  1. A. B
  2. B. B$_2$H$_6$
  3. C. B$_2$O$_3$
  4. D. HBF$_4$
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:B, C

Solution

Boron nitride (BN) forms from boron-containing species that have B-O or B-H bonds reactive with NH$_3$ at high temperature.

(A) B (elemental boron) alone is NOT a compound; the question stem asks for compounds reacting with NH$_3$. Elemental boron does react with N$_2$ at high temperature to give BN, but with NH$_3$ this is conventionally not the standard preparation; and 'B' is not a compound. (A) is WRONG by the FIITJEE rationale (not a compound).

(B) Diborane: 3 B$_2$H$_6$ + 6 NH$_3$ $\rightarrow$ 2 B$_3$N$_3$H$_6$ (borazine, 'inorganic benzene'); on strong heating borazine converts to BN. So diborane + NH$_3$ ultimately gives BN. (B) is CORRECT.

(C) B$_2$O$_3$ + 2 NH$_3$ $\xrightarrow{\text{high T}}$ 2 BN + 3 H$_2$O. Standard high-temperature preparation. (C) is CORRECT.

(D) HBF$_4$ (fluoroboric acid) + NH$_3$ does not give BN under normal conditions (it just gives the ammonium tetrafluoroborate salt NH$_4$BF$_4$). (D) is WRONG.

Correct options: B, C.

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