Question

$B_{2}C{a}_6{O}_{11}+N{a}_{2}C{O}_3\stackrel{\Delta }{\to }\left[X\right]+CaC{O}_3+NaB{O}_2$ (unbalanced equation)
Correct choice(s) for [X] is/are:

• A. structure of anion of crystalline [X] has one boron atom sp${}^3$ hybridised and other three boron atoms sp${}^2$
  hybridised
• B. X with NaOH (aq.) gives a compound which on reaction with hydrogen peroxide in alkaline medium yields
  a compound used as brightner in soaps
• C. hydrolysis of [X] with HCl or H${}_2$SO${}_4$ yields a compound which on reaction with HF gives fluoroboric acid
• D. [X] on heating with chromium salts in oxidising flame gives green coloured bead in cold

Answer 1

Answer: (B), (C), (D)

[X] on heating with chromium salts in oxidising flame gives green coloured bead in cold
X with NaOH (aq.) gives a compound which on reaction with hydrogen peroxide in alkaline medium yields
a compound used as brightner in soaps
hydrolysis of [X] with HCl or H${}_2$SO${}_4$ yields a compound which on reaction with HF gives fluoroboric acid

Compound [X] is Na${}_2$B${}_4$O${}_7$
(A) two boron atoms are $s{p}^2$ while other two boron atoms are $s{p}^3$ hybridised.
(B) product is sodium peroxoborate which is used as brightner in soaps.
(C) $H_{3}B{O}_3$ is formed which with HF gives $HB{F}_4$.
(D) Green bead in oxidising as well as in reducing flame in cold.