In aqueous solution on hydrolysis of borax produces NaOH and H3BO3.
Na2B4O7 + 7H2O → 4H3BO3 + 2NaOH
H3BO3 is a weak acid but NaOH is strong base. Thus in aqueous solution of borax, basic property will predominate. Hence in aqueous solution pH of the solution will be more than 7.