Answer
Structure A has the lowest formal charges.
Work Step by Step
Structure A has a formal charge of 0 on all atoms, as shown in the calculations below:
F.C. = (# of Valence e-) - (Number of Bonds) - (Number of e- in lone pairs)
For C: F.C. = 4 - 4 - 0 = 0
For O: F.C. = 6 - 2 - 4 = 0
For Cl: F.C. = 7 - 1 - 6 = 0
