The element group which is least likely to form ions is 4A group
explanation
Element of group 4A has 4 valence electrons. for example Carbon which has [He] 2S2 2P2 electron configuration has 4 valence electrons.
Since 4A elements has 4 valence electrons , it means that their valence shell is half filled which is relatively stable. For this reason 4A element readily form ions.
