Regarding the chemistry of boron and…

Regarding the chemistry of boron and its compounds, the correct statement(s) is/are

One or more options correct

Regarding the chemistry of boron and its compounds, the correct statement(s) is/are

A. In $\mathrm{B_2H_6}$ the two bridging $\mathrm{B\!-\!H\!-\!B}$ units are three-centre two-electron bonds, whereas the four terminal $\mathrm{B\!-\!H}$ bonds are two-centre two-electron bonds.
B. Towards $\mathrm{NH_3}$ the Lewis acidity follows $\mathrm{BF_3}>\mathrm{BCl_3}>\mathrm{BBr_3}$ because the electronegativity of the halogen decreases down the group.
C. Borazine, $\mathrm{B_3N_3H_6}$ , adds three molecules of $\mathrm{HCl}$ to give $\mathrm{B_3N_3H_9Cl_3}$ in which each chlorine is attached to a boron atom.
D. Heating borax, $\mathrm{Na_2B_4O_7\cdot10H_2O}$ , gives a glassy mass of $\mathrm{NaBO_2}$ and $\mathrm{B_2O_3}$ , which on fusion with a $\mathrm{Cu^{2+}}$ salt in the oxidising flame gives a blue bead of $\mathrm{Cu(BO_2)_2}$ .

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Answer: A, C, D

(A) True. Diborane has 12 valence electrons; four terminal

\mathrm{B-H}

bonds use 8, leaving 4 electrons for two bridging three-centre two-electron bonds.
(B) False. The order is

\mathrm{BF_3}<\mathrm{BCl_3}<\mathrm{BBr_3}

. Back-donation of the lone pair of

2p

fluorine into the empty

2p

orbital of boron is most efficient because of the good

2p

2p

overlap, which reduces the electron deficiency of boron in

\mathrm{BF_3}

; the electronegativity argument is overridden.
(C) True. Polar

\mathrm{B^{\delta+}-N^{\delta-}}

bonds add

\mathrm{H^{+}}

to nitrogen and

\mathrm{Cl^-}

to boron, giving

\mathrm{B_3N_3H_9Cl_3}

with

\mathrm{B-Cl}

and

\mathrm{N-H}

bonds.
(D) True. Borax on heating loses water and gives

\mathrm{Na_2B_4O_7\to 2NaBO_2+B_2O_3}

;

\mathrm{B_2O_3}

combines with

\mathrm{CuO}

to give blue copper(II) metaborate (borax-bead test).
Correct: A, C, D.

Original question written in the JEE Advanced 2023 Paper 1 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake