How many electrons does chlorine (Cl) have in its outer shell?

Chlorine (Cl) is an element located in group 17 of the periodic table, which is also known as the halogens. Elements in this group are characterized by having seven electrons in their outermost electron shell, or valence shell. The electron configuration of chlorine is [Ne] 3s² 3p⁵, meaning it has two electrons in the 3s subshell and five electrons in the 3p subshell, totaling seven valence electrons.

This configuration is important because it explains chlorine's reactivity; the element tends to gain one additional electron to achieve a stable octet configuration, resembling that of the noble gases. Therefore, the number of electrons in the outer shell of chlorine is indeed seven, making this the correct choice.