Question

What would be a larger K (parent atom) or ${{K}^{+}}$?

Answer 1

Before answering this question, we should know what finds out the atomic size and then apply the same theory for ionic size. The outermost electrons (electrons that are on the highest energy level) determine the size of an atom.

Complete answer:
In other words, the farther the electron is from the nucleus, the more will be the atomic size.
We know, Electrons are present in the orbitals which have various energy levels. The distance between the outermost electron and nucleus depends on the energy level. The higher the energy level, the more is the distance between the outermost electron and the nucleus.
For Example :
Potassium, K is located in period 4, Group 1 of the periodic table that tells the number of electrons it has on its highest energy level is 1.
The neutral potassium atom has an electronic configuration:
$K:1{{s}^{2}}\,2{{s}^{2}}\,2{{p}^{6}}\,3{{s}^{2}}\,3{{p}^{6}}\,4{{s}^{1}}$
The outermost electron that lies on the highest energy level tells us about the size of the potassium atom. So, It lies on the fourth energy level from the nucleus.
When a potassium atom loses the outermost electron, a potassium ion is formed.
The potassium ion has an electronic configuration:
${{K}^{+}}:1{{s}^{2}}\,2{{s}^{2}}\,2{{p}^{6}}\,3{{s}^{2}}\,3{{p}^{6}}$
Here, the outermost electrons lie on the third energy level that is closer to the nucleus. This tells that the potassium ion is smaller in size compared to the potassium atom.

Note:
Cations are the molecules or atoms that have lost an electron or more than one electron which gives a net posture charge on the atom. It happens because the number of protons in the atom is more than the number of electrons. That snatches the neutrality of an atom and due to the loss of an electron, a cation is formed