Halogens have ______ electrons in their outermost shells.

seven

The correct answer is option 4. seven.

Halogens are a group of elements located in Group 17 of the periodic table. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements are characterized by having seven electrons in their outermost electron shells.

1. Electronic Configuration:

Halogens belong to Group 17, also known as the halogen or Group VIIA group. They have the general electronic configuration \( ns^2 np^5 \), where \( n \) is the principal quantum number corresponding to the outermost shell.

2. Outermost Shell:

The outermost electron shell of halogens is the \( p \)-shell, and it contains five electrons (represented by \( np^5 \)). Since the \( p \)-shell can accommodate a maximum of six electrons, halogens need one more electron to achieve a stable, full outer shell.

In summary, halogens have seven electrons in their outermost electron shells, and their reactivity stems from their tendency to gain one electron to achieve a stable, noble gas-like configuration with eight electrons in the outermost shell.