Answer:
the size of Ca is the greatest ,then Mg is the greater on size than Be
Explanation:
if you make the electron configuration for each of the elements, what is the main difference u gonna see ?
Be 4 1s2/2s2
Mg 12 1s2 /2s2 2p6/3s2
Ca 20 1s2 /2s2 2p6/3s2 3p6 3d/4s2
see that all the elements are in the same group but are in different period
u gonna see the last electron valance shell in Ca are too far from its nucleus but in Be the last electrons are too close and more attracted to the atom's nucleus , so the size of Ca is the biggest then Mg then Be
