An aqueous solution of borax is :

The chemical formula for borax is ${\mathrm{Na}}_2{ \mathrm{B}}_4{\mathrm{O}}_7$, often known as sodium tetraborate.
Following is a diagram illustrating the entire reaction between borax and water;

${\mathrm{Na}}_2{ \mathrm{B}}_4{\mathrm{O}}_7+7{\mathrm{H}}_2\mathrm{O}\to 2\mathrm{NaOH}+4{\mathrm{H}}_3{\mathrm{BO}}_3$
Boric acid ${\mathrm{H}}_3{\mathrm{BO}}_3$ and sodium hydroxide NaOH, both strong bases, are produced as a result of the reaction.
The total reaction produces a weak acid and a strong base, which changes the composition of the solution.