Question

Pick the correct statement
(i) Borax is white crystalline solid containing
${\left[B_4{O}_5(OH{)}_4\right]}^{2-}$ units.
(ii) Aqueous solution of borax is acidic in nature.
(iii) Cobalt gives blue colour in borax bead test.

• A. (i) and (ii)
• B. (i) and (iii)
• C. (ii) only
• D. (ii) and (iii)

Answer 1

Answer: (B)

1. Structural formula of borax $\left(N{a}_2{B}_4{O}_7\cdot 10H_{2}O\right)$ is
$N{a}_2\left[B_4{O}_5(OH{)}_4\right]\cdot 8H_{2}O\Rightarrow$ correct statement.
II. Aqueous solution of borax is basic in nature, because borax in water dissociates into $H_{3}B{O}_3$ (weak acid) and $NaOH$ (strong base).
$N{a}_2{B}_4{O}_7+7H_{2}O\to 4H_{3}B{O}_3+2NaOH\Rightarrow$ Incorrect statement.
III. Cobalt (Co) gives blue colour of cobalt metaborate $\left[Co{\left(B{O}_2\right)}_2\right]$ in borax bead $\left(NaB{O}_2+B_2{O}_3\right)$ test $\Rightarrow$ Correct statement.
So, the correct statements are $(I)$ and $(|I|)$.