Which of the following structures is the most preferred and hence of lowest energy of SO₃ ? 

• 
• 
• 
• 

D.

Formal charges help in the selection of the lowest energy structure from a number of possible energy structure from a number of possible Lewis structures for a given species. Generally, the lowest energy structure is the one with the smallest formal charges on the atoms. 

Formal charge on an atom: = total number of valence electrons- non - bonding electrons - 1/2 x bonding electrons.

For lewis structure of SO₃



Formal charge on three O atoms