The central atom in a lewis structure tends to be the atom.

The central atom in a lewis structure tends to be the least electronegative atom.

Explanation:

Lewis structures show each atom and its position in the structure of the molecule using its chemical symbol.

In Lewis structure, the central atom tends to be the least electronegative atom. Usually the central atom will be the one that has the most unpaired valence electrons or  least electronegative.

Therefore, the best phrase that completes the sentence is "least electronegative".

The central atom is also usually the least electronegative.

Explanation:

The central atom is usually the least electronegative element in the molecule or ion; hydrogen and the halogens are usually terminal.

The least electronegative elements in the center of lewis structures because an atom in the central position shares more of its electrons than does a terminal atom. Atoms with higher electronegative are generally more reluctant to share its electrons.

28. evolution

29. environment, survive, offspring  

explanation:

colorectal cancer may also develop from areas of abnormal cells in the lining of the colon or rectum. this area of abnormal cells is called dysplasia and is more commonly seen in people with certain inflammatory diseases of the bowel such as crohn's disease or ulcerative colitis.