What is the position of an element in the periodic table if its electron configuration is 1s^2 2s^2 2p^6 3s^2 3p^5

Cl  chlorine

Chlorine is located in 7A group of the third period.

[Ne]3s²3p⁵
2+5=7

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.