When aqueous solutions of borax is acidified with $\mathrm{HCl}$, we get

When aqueous solution of borax $\left({\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7\right)$ is acidified
with $\mathrm{HCl}$, we get ${\mathrm{H}}_3{\mathrm{BO}}_3$ and $\mathrm{NaCl}$ as follows

$\underset{\mathrm{Borox}}{{\mathrm{Na}}_2{\mathrm{B}}_4{\mathrm{O}}_7}+2\mathrm{HCl}+5{\mathrm{H}}_2\mathrm{O}⟶2\mathrm{NaCl}+\underset{\mathrm{Boric} \mathrm{acid}}{4{\mathrm{H}}_3{\mathrm{BO}}_3}$

Boric acid is not a proticacid it does not give ${\mathrm{H}}^{+}$ ion accepts a pair of electrons and acts as a Lewis acid.