a)\(4R+3O2-->2R2O3\)
\(m_{O2}=m_{R2O3}-m_R=3,06-1,62=1,44\left(g\right)\)
\(n_{O2}=\frac{1,44}{32}=0,045\left(mol\right)\)
\(n_R=\frac{4}{3}n_{O2}=0,06\left(mol\right)\)
\(M_R=\frac{1,62}{0,06}=27\left(Al\right)\)
=.CTHH:Al2O3
b) X là oxit bazơ