${\mathrm{B}}_2{\mathrm{H}}_6+{\mathrm{NH}}_3\to \mathrm{X}$ (ionic compound) $\stackrel{\mathrm{heated}}{\to }\text{Y}+{\mathrm{H}}_2\uparrow$ Find total number of sp² hybridised atoms per Y molecule.

The complete reaction is,

${\mathrm{B}}_2{\mathrm{H}}_6+2{\mathrm{NH}}_3\to {\mathrm{B}}_2{\mathrm{H}}_6.2{\mathrm{NH}}_3$ (ionic compound) $\stackrel{\mathrm{heated}}{\to }{\mathrm{B}}_2{\mathrm{N}}_3{\mathrm{H}}_6+{\mathrm{H}}_2\uparrow$ 

So,

$\mathrm{Y}\to {\mathrm{B}}_2{\mathrm{N}}_3{\mathrm{H}}_6$

The total number of sp² hybridised atoms per ${\mathrm{B}}_2{\mathrm{N}}_3{\mathrm{H}}_6$ molecule is 6.