JEE Advanced · 2016 · 22 May 2016 · Paper 1 · p-Block Elements

Borax (${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\cdot 10{\mathrm{H}}_2\mathrm{O}$) contains the tetraborate anion $[{\mathrm{B}}_4{\mathrm{O}}_5(\mathrm{OH}{)}_4{]}^{2-}$. (A) is correct: it has four boron atoms. (B) is incorrect: the structure is three-dimensional, not planar. (C) is correct: two boron atoms are $s{p}^2$ hybridized (trigonal planar) and two are $s{p}^3$ hybridized (tetrahedral). (D) is correct: each boron has one terminal OH group.