Elements like barium located toward thr bottom of a group have a lower attraction for their valence electrons because they have a

Barium has a lower attraction for their valence electrons because there are a large number of electrons between the valence electrons and nucleus. And these electron cause great repulsion.

Explanation:

Barium is an alkaline earth metal and it's atomic number is 56 with electronic configuration [tex]1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^{10}5s^{2}5p^{6}6s^{2}.

This results in more number of shells in a barium atom. Hence, valence shell moves far away from the nucleus due to this there is very less attraction between the valence electrons and nucleus of Ba atom.

Thus, we can conclude that elements like barium located toward the bottom of a group have a lower attraction for their valence electrons because they have greater atomic mass.

b. the carbon cycle ensures living things have a source of hydrogen

cell division is not regulated in tumor cells.