\(n_{O_2}=\dfrac{1,232}{22,4}=0,055\left(mol\right)\\ 4R+3O_2\rightarrow\left(t^o\right)2R_2O_3\\ n_R=\dfrac{4}{3}.0,055=\dfrac{11}{150}\left(mol\right)\\ \Rightarrow M_R=\dfrac{22,7}{\dfrac{11}{150}}\approx309,545\left(\dfrac{g}{mol}\right)\)
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