$\text{ Colemanite }+{\mathrm{Na}}_2{\mathrm{CO}}_3⟶\left(B\right)+\left(C\right)+\left(D\right)$

                                                   (White ppt.)

$\left(D\right)\stackrel{{\mathrm{CO}}_2}{⟶}\left(C\right)+{\mathrm{Na}}_2{\mathrm{CO}}_3$ $\stackrel{\text{ recryвtallisation }}{\to }$$C$'

$C$'  has only 8 water molecules of crystallisation Number of $s{p}^3$ hybridised atoms in compound $C$' 

$C^{\mathrm{\prime }}\to {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\cdot 10{\mathrm{H}}_2\mathrm{O}$ or ${\mathrm{Na}}_2\left[{\mathrm{B}}_4{\mathrm{O}}_5(\mathrm{OH}{)}_4\right]\cdot 8{\mathrm{H}}_2\mathrm{O}$

$s{p}^3\text{ atoms }\Rightarrow 8+9+2=19$

Reaction:

${\mathrm{Ca}}_2{\mathrm{B}}_6{\mathrm{O}}_{11}+2{\mathrm{Na}}_2{\mathrm{CO}}_3\to \underset{\text{ (White ppt.) }}{2{\mathrm{CaCO}}_3}+{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7+2{\mathrm{NaBO}}_2$

${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7+{\mathrm{NaBO}}_2\underset{\mathrm{out} \mathrm{and} \mathrm{filtered}}{\overset{\mathrm{Conc}. \mathrm{and} \mathrm{allowed} \mathrm{to} \mathrm{crystallization}}{\to }}\underset{\mathrm{In} \mathrm{filtered}}{{\mathrm{NaBO}}_2}+\underset{\mathrm{as} \mathrm{residue}}{{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7}\cdot 10{\mathrm{H}}_2\mathrm{O}$$$\begin{gathered} \underset{\mathrm{crytallization} \mathrm{out} \mathrm{again}}{\overset{{\mathrm{CO}}_2 \mathrm{passed} \mathrm{and} }{\to }}{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\cdot 10{\mathrm{H}}_2\mathrm{O}\downarrow \\ 4{\mathrm{NaBO}}_2+{\mathrm{CO}}_2\to {\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7+{\mathrm{Na}}_2{\mathrm{CO}}_3 \end{gathered}$$