Question

Given below are a few elements: Li, K, Cs, F.
Identify the element which:
(a) has the least atomic radius.
(b) has two valence electrons.
(c) is the most electropositive.

Hint:

Cesium is so electropositive and reactive that it will explode upon contact with even cold water or ice!

Answer 1

(a) Fluorine (F): Fluorine is in Period 2 and Group 17. Compared to the alkali metals listed (Li, K, Cs), it has more protons in the same/fewer shells, pulling the electrons closer.
(b) None of these: Li, K, and Cs are Group 1 elements (1 valence electron). F is a Group 17 element (7 valence electrons).
(c) Cesium (Cs): Electropositivity (metallic character) increases down a group. Since Cesium is at the bottom of Group 1 among the choices, it loses its valence electron most easily.