The following ions contain the same number of electrons. Rank them in order of decreasing ionic radii. Rank from largest to smallest radius. To rank items as equivalent, overlap them. K^+,Sc^3+,Cl^-,S^2-,P^3-

P^3-  >  S^2-  >  Cl^- > K^+ >  Sc^3+

Explanation:

Ionic radii is an example of physical properties of Periodicity.

The size of an atom's ion is difficult to estimate because of the electronic distribution and arrangement. This is due to the fact that the atom' ion have no definite outer boundary. In order to circumvent this problem, the atom's ion is estimated in a crystal lattice in terms of its ionic radii.

Ionic radii is taken as half the distance between atomic ions in a crystal lattice. Across a period in the periodic table , ionic radii decreases progressively from left to right.

Down the group, the ionic radius increases from top to bottom.

So the arrangement of the given elements from largest to smallest radius in the decreasing order of ionic radius will be:

P^3-  >  S^2-  >  Cl^- > K^+ >  Sc^3+

it is stable as it is in group 0 which have full outer shells of electrons