Ответ:

Mr(BaSO4) = 137 + 32 + 16*4 = 233

W(Ba) = Ar(Ba) * n / Mr(BaSO4) *100% = 137 *1 / 233 *100% = 59%

W(S) = Ar(S) * n / Mr(BaSO4) *100% = 32 * 1 / 233 *100% = 14%

W(O) = Ar(O) * n / Mr(BaSO4) *100% = 16 * 4/ 233 *100% = 27%