Question

Arrange the following cations in order of decreasing size,Ra+2,Se+2,Ca+2,Ba+2 ?

Answer 1

,Ra+2,Se+2,Ca+2,Ba+2 ?

I would rank these in size from large to small as
Ra^2+
Ba^2+
Ca^2+
Se^2+
You should Google and confirm.
As one goes down the periodic table in a column size increases.
As one goes across the periodic left to right the size decreases. Ca and Se are in the same period