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

We are given the elements: Li, K, Cs, F

Let us identify each part step by step.

(a) Element having the least atomic radius:
Atomic radius decreases from left to right across a period and increases from top to bottom in a group.
Among Li, K, Cs and F, fluorine (F) is the smallest atom because it is placed in Period 2 and towards the right side of the periodic table.
Therefore, the element with the least atomic radius is F.

(b) Element having two valence electrons:
Let us check the valence electrons of each given element:
Li = 1 valence electron
K = 1 valence electron
Cs = 1 valence electron
F = 7 valence electrons

So, none of these elements has two valence electrons.

(c) Element which is the most electropositive:
Electropositive character increases down a group because the outer electron is farther from the nucleus and can be lost more easily.
Li, K and Cs all belong to Group 1, but cesium (Cs) lies lowest among them.
Therefore, Cs is the most electropositive element.

Final Answers:
(a) F
(b) None of these
(c) Cs