a) \(PTK_{X_2O_3}=PTK_{CaO}+2NTK_{Na}=56+2\times23=102\left(đvC\right)\)
b) Ta có: \(2NTK_X+3NTK_O=102\)
\(\Leftrightarrow2NTK_X+3\times16=102\)
\(\Leftrightarrow2NTK_X+48=102\)
\(\Leftrightarrow NTK_X=\frac{102-48}{2}=27\left(đvC\right)\)
Vậy X là nhôm Al