Which one of the following atoms has the largest radius? ова осо oca

Ba

Explanation:

The elements  Calcium ( Ca ) and Cobalt ( Co ) , are both present in the same period , and across the period the atomic radius decreases from left to right , since , the atomic number increases , so the electrons increases , which in turns increases the effective nuclear charge , and hence the size decreases ,

Therefore ,

Calcium will have bigger atomic radii as compared to Cobalt .

Now,

The elements Barium ( Ba ) and Calcium ( Ca ) are , both are present in the same group , and down the group , atomic radii increases , since , as going down the group , the atomic number increase , so the shells increases , hence the size increases .

Therefore , the atom with the largest radii is Barium .