The entire 1st group on the table.
The reason behind this is the amount of valence electrons each of them have.
Chlorine has 7 v.e's meaning it needs one v.e.
This works perfectly as alkali metals have 1 v.e.
They come together to form ionic bonds, like things like NaCl (table salt) or KCl.
Hope this helps, and let me know if you have any further questions.