Borax in water givesB4O72− + 7H2O →  4H3BO3+2OH−How many grams of Borax Na2B4O7. 10H2O are required to prepare 50 ml of 0.2 M solution.

The n-factor or valency factor of borax in the above reaction is 2Meq. of borax in 50 ml solution = VN = 50 x 0.2 x 2 = 20Let weight of borax required = W   WE=NV1000W382 × 2 × 1000 =20∴   WNa2B4O7. 10H2O = 3.82