Bài $1:$
$*)M_{R_2O_n}=60\Rightarrow 2M_R+nM_O=60\Rightarrow 2M_R+16n=60\Rightarrow n<3,75$
$\Rightarrow n \epsilon (1 ;2 ; 3)$
$*)R_2O\Rightarrow M_R=22 loai$$*)RO\Rightarrow M_R=40\Rightarrow Ca\Rightarrow CaO$
$*)R_2O_3\Rightarrow M_R=6\Rightarrow loai$