Aqueous solution containing 1 mol of borax reacts with 2 mol of acids. This is because of
formation of 2 mol of BOH3 only
formation of 2 mol of BOH4- only
formation of 1 mol each of BOH3 and BOH4-
formation of 2 mol each of BOH4- and BOH3, of which only BOH4- reacts with acid
B4O5OH42- + 5H2O ⇌ 2BOH3 weak acid + 2BOH4- salt