JEE Main 2022 · 26 July · morning · Single correct · +4 / −1
Borazine, also known as inorganic benzene, can be prepared by the reaction of 3-equivalents of "X" with 6-equivalents of "Y". "X" and "Y", respectively are :
- (a) B(OH)₃ and NH₃
- (b) B₂ H₆ and NH₃
- (c) B₂ H₆ and HN₃
- (d) NH₃ and B₂ O₃
Answer and solution
Answer (b) B₂ H₆ and NH₃
Solution
Chemistry ma’am · 4 steps
Borazine needs B–H and N–H bonds, so take diborane for boron and ammonia for nitrogen.
- Look at borazine. Borazine, B₃N₃H₆, is a six-membered ring of alternating B and N atoms. Every B carries one H and every N carries one H. So the boron source must already have B–H bonds, and the nitrogen source must have N–H bonds.
- Pick the reagents. Diborane, B₂H₆, supplies boron with B–H bonds. Ammonia, NH₃, supplies nitrogen with N–H bonds. They first form an adduct, [BH₂(NH₃)₂]⁺[BH₄]⁻, which loses H₂ on heating.
3B₂H₆ + 6NH₃ → 3[BH₂(NH₃)₂]⁺[BH₄]⁻ →(Δ) 2B₃N₃H₆ + 12H₂
- Check the count. Left side: 6 B, 6 N and 18 + 18 = 36 H. Right side: 6 B, 6 N and 12 + 24 = 36 H. The ratio is 3 of B₂H₆ to 6 of NH₃, as the question says.
- So. X is B₂H₆ and Y is NH₃, which is option (b).
The idea to keep. For borazine, remember the pair diborane plus ammonia in a 1 : 2 ratio, heated so that H₂ leaves. The B–H and N–H bonds in the ring come straight from these two reagents.
Answer from the NTA final answer key. Solution by PrepWiser.