Дано
m(K2O) = 18.8 kg
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m(Na2O)-?
M(K2O)= 94 g/mol
N(K2O) = (m/M)*N(A) = 18.8 / 94 * 6.02*10^23 = 1.204 *10^23 молекул
N(K2O)=N(Na2O)
M(Na2O) = 62 g/mol
m(Na2O)= N(Na2O) * M(Na2O) / N(A)
m(Na2O)= 1.204*10^23 * 62 / 6.02*10^23 = 12.4 g
ответ 12.4 г