The charge on a potassium ion in its ionic compounds is...

2+
1+ or
various charges

Potassium has the arrangement of 2,8,8,1 and it likely to lose its outer electron to a more electronegative element such as a non-metal
It will become a positive ion with the stable electron arrangement of 2,8,8

As the nucleus still has 19 protons (19 + charges) and only 18 electrons (18 - charges), it will be an ion with an overall 1+ charge, K+. This is typical of group 1 elements

What happens to the size?

Well the outer shell is lost, so the ion has only 3 shells and it smaller.

As there are more protons than electrons, the electrons are held more tightly and the electrons are held closer to the nucleus making it even smaller.

NB Positive ions are smaller than the atom from which they are made. Ionic radius is smaller than than atomic radius for positive ions.

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