How many electrons do all halogen atoms need to fill their outer energy level?

Seven

Explanation:

Because all halogens have seven valence electrons, they are "eager" to gain one more electron. Doing so gives them a full outer energy level, which is the most stable arrangement of electrons. Halogens often combine with alkali metals in group 1 of the periodic table.

Halogens only need one electron to complete their valkance shells.

Explanation:

Halogens are present in the VIIA group of the periodic table so seven electrons are already present. one is needed to become stable.