Ответ:

Mr(Al2O3) = 27*2 + 16*3 =102

W(O) = Ar(O) *n / Mr(Al2O3)  *100% = 16*3 / 102  *100% =47%

Mr(K2O) = 39*2 + 16 =94

W(O) = Ar(O) *n / Mr(K2O)  *100% = 16*1 / 94  *100% =17%

Mr(ZnO) = 65+16 = 81

W(O) = Ar(O) *n / Mr(ZnO)  *100% = 16*1 / 81  *100% =20%