The alkali metal that joins with a halogen group to form table salt is sodium (Na).

Here's the breakdown:

* Sodium (Na) is an alkali metal, found in Group 1 of the periodic table.

* Chlorine (Cl) is a halogen, found in Group 17 of the periodic table.

When sodium and chlorine react, they form sodium chloride (NaCl), which is the chemical name for table salt.