Gọi nguyên tố halogen đó là X
Các PTHH:
\(2Na+X_2-t^o\rightarrow2NaX\)
.....\(\dfrac{11,7}{2\left(23+X\right)}\)......\(\dfrac{11,7}{23+X}\).....(mol)
\(2Al+3X_2-t^o\rightarrow2AlX_3\)
....\(\dfrac{8,9.3}{2\left(27+3X\right)}\).....\(\dfrac{8,9}{27+3X}\).......(mol)
Ta có: \(\dfrac{11,7}{2\left(23+X\right)}=\dfrac{8,9.3}{2\left(27+3X\right)}\)
\(\Leftrightarrow\) X = 35,5 (Clo) \(\Rightarrow\) Halogen đó là clo