Question

How many electrons are possessed by `K^+` ion?

Answer 1

Well it has got 18 electrons....

Explanation:

We gots `K^+`, an alkali metal cation.

The parent atom is potassium, for which `Z=19`, the which means that there are 19 massive, formally positively charged nuclei in the potassium nucleus....this is what defines the nucleus as potassium

And for every positive charge, in the NEUTRAL material, there must be an equal and opposite NEGATIVE charge, and these are the electrons that are conceived to whizz around the nuclear core. If we got `K^+`, there must be ONE electron less than 19....and so, formally, potassium has a Noble Gas configuration, 18 electrons in total, isoelectronic with argon.....

The Periodic Table in front of you now (and surely there must be one in front of you if you are doing your chemistry homework!), gives the atomic (and electronic) numbers, and the average atomic masses, for the 100 or so known elements.

How many electrons in `Ca^(2+)`; how many nucular protons?

See this older answer and links for more of the same.