The compound present in borax bead is :

The reaction to find the borex bead is,${\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\cdot 10{\mathrm{H}}_2\mathrm{O}\stackrel{\mathrm{\Delta }}{⟶}{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\stackrel{\mathrm{\Delta }}{⟶}\underset{ \mathrm{Borax} \mathrm{bead}}{\underbrace{2{\mathrm{NaBO}}_2+{\mathrm{B}}_2{\mathrm{O}}_3}}$

Thus, the borex bead is ${\mathrm{NaBO}}_2+{\mathrm{B}}_2{\mathrm{O}}_3$ .