Ответ:

дано

m(Al2O3) = 204 g

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m(Al)-?

4Al+3O2—>2Al2O3

M(Al2O3) =102 g/mol

n(Al2O3) = m/M = 204/ 102 = 2 mol

4n(Al) = 2n(AL2O3)

n(Al) = 4 mol

M(Al) = 27 g/mol

m(Al) = n*M = 4*27 = 108 g

ответ 108 г