Which of the following molecules has a double bond?

Question

1. NO3- 4. H2
2. C2H4 5. C12
3. SO2 6. None of the previous answers

I got that three of these molecules have a double bond (NO3-, SO2, and C2H4), but the answer is one. I am thinking that maybe the professor wants C2H4 because it is the "clearest cut" double bond?

Answer 1

Yes and No. The answer is 1 and that is C2H4. The so-called "double bond" in NO3^- and SO2 are not real double bonds although we draw double bonds with the Lewis dot structure. Remember that there are resonance forms so these double bonds are only figments of our imagination. In real life they are somewhere between a single bond and double bond and all of the bonds are equal.