How does an atom of potassium - 41 became a potassium ion with a+1

Answer: by loosing an electron

Explanation:

An atom of potassium is a neutral atom, containing 19 protons and 19 electrons (neutral atoms have equal number of protons and electrons).

According to its electron configuration, the atom of potassium has only one electron in its outest shell (the orbital which is farthest from the nucleus) : therefore, it easily loose this electron, giving it to atoms of other elements. When the atom of potassium loses this electron, it becomes a positive ion, with charge + 1, because now it has 19 protons and 18 electrons only.