Here's why:

* Borax (sodium borate) is a compound formed when a weak acid (boric acid) reacts with a strong base (sodium hydroxide).

* When dissolved in water, borax undergoes hydrolysis, meaning it reacts with water to form both a weak acid (boric acid) and a weak base (sodium hydroxide).

* This makes borax a weak base in solution.

However, it's important to remember that borax is not inherently a base or an acid. It's a salt that can act as a weak base in aqueous solutions.