Why is the symbol [Ar] used in the electron configuration of potassium, and what does it represent?

To denote a stable inner configuration and it represents argon

Explanation:

The symbol [Ar] used in the electron configuration of potassium represents the inner electronic configuration of the element.

This argon atom is stable octet with completely filled shells. Most noble gases are used to write the electronic configuration of other atoms. The inner atomic orbitals of elements are similar to those of nearby noble gases.

i'm assuming that the correct answer is indeed the first one/ "a"..

it is b that is the answer.