JEE Advanced 2016 · Paper 1 · Chemistry Q26

ChemistryMultiple correct+4 / -2Question 26 of 54

The crystalline form of borax has

tetranuclear

\ce{[B4O5(OH)4]^{2-}}

unit

all boron atoms in the same plane

equal number of

sp^2

and

sp^3

hybridized boron atoms

one terminal hydroxide per boron atom

Answer and worked solution

Official answer: A, C, D

Structure of borax. Borax, $\ce{Na2[B4O5(OH)4].8H2O}$ , contains the tetranuclear $\ce{[B4O5(OH)4]^{2-}}$ ion. (A) is true.

Two borons are trigonal ( $sp^2$ , $\ce{BO3}$ ) and two are tetrahedral ( $sp^3$ , $\ce{BO4}$ ). (C) is true.
The tetrahedral borons make the unit puckered, so the four borons are not coplanar. (B) is false.
Each boron carries exactly one terminal OH. (D) is true.

(A), (C), (D)

Topics:Group 13 Hybridisation

JEE Advanced 2016 · Paper 1, Chemistry question 26