the question: Why is the Lewis dot sturucture with the smallest possible charges the best contributor?
Since an species with an excess charge on it is not stablilized i.e there is not enough positive charge or negative charge to stabilize it. For example if an species has a formal charge of +2 compared to +1 then the one with +2 formal charge is less stable since it is in need of more negative charge than the one that has +1 charge. Now let me point out what is wrong with question #1 of module 25, even though the answer given is correct. Inorder to write valid Lewis dot sturtures you first have to count the valence electrons involved. And only these valence electrons must be shown on the Lewis dot sturucture. Here for O3 the total valence electrons must be (6 + 6 + 6) = 18. If you are showing different resonace forms (i.e. different Lewis dot structures for the same molecule or ion) each of them must have these total valence electrons (18 electrons) to be valid. In this case Lewis dot structure #1 and #2 have 18 valence electrons however Lewis dot structure #3 and #4 do not and therefor
