Explanation:

- Halogens have seven electrons in their outermost shells.

- These are highly reactive non-metals found in Group 17 of the periodic table.

- They need one more electron to achieve a full outer shell, which typically holds eight electrons.

- Option 1: Halogens with one electron would resemble alkali metals, not halogens.

- Option 2: Halogens do not have eight electrons unless they gain one electron, resulting in a full outer shell resembling noble gases.

- Option 3: Five electrons would make them similar to Group 15 elements like nitrogen and phosphorus.

- Correct Answer: Option 4 - seven