W(k)= 39,7% w(mn)= 27,9% w (0)- остальное формула -?

W (O) = 100% - 39.7% - 27.9% = 32.4%

32.4% = 0.324
39.7% = 0.397
27.9% = 0.279

n (K) = 0.397 / 39 = 0.01018
n (Mn) = 0.279 / 55 = 0.00507 моль
n (O) = 0.324 / 16 = 0.02025 моль

n (K) : n (Mn) : n (O) = 2 : 1 : 4 => K2MnO4

ответ: K2MnO4