Объяснение:
Mr(H2O) = 1*2 + 16 = 18
W(H) = Ar(H) *n / Mr(H2O) *100% = 1*2 / 18 *100% =11%
W(O) = Ar(O) *n / Mr(H2O) *100% = 16*1 / 18 *100% =89%
