How is potassium bigger than barium in size - Chemistry - Classification of Elements and Periodicity in Properties

Question

How is potassium bigger than barium in size?

Priya G N · Accepted Answer

As we move across the period atomic size and ionic radii decreases
If we compare Potassium (K) 19 with calcium (Ca) 20, we can say
that there is large difference in the ionic radii value for
potassium (152) and calcium (114) Hence calcium is smaller than
potassium

But as we move down the group, atomic size and ionic radii
increases If we compare potassium and barium, Potassium

(K 19) has ionic radii (152), while barium (Ba 56) has ionic radii
(149), there is no much difference and both almost have the same
size with potassium being little bigger