Chemistry-resonance structures

Question

what molecules have resonance structure? There should be 3.

HCN, SeF6, NO2-, AsF5, XeF2, TeF5-, H2CO, SF4, XeF4, PO43-, BrF3, NH3, CH3NH2, SF5+, and C2H2.

I think NO2-, PO43-(Chrome said that it is, but then shouldn't SeF6 and AsF5 also have resonance structures? This is where I am most confused) have resonance structures.

please pick out the 3 molecules. I have a test tmrw...

Answer 1

No, for SeF6 and AsF5 as there are no double bonds. Both NO2- and PO43- have double bonds. The other one would be H2CO (formaldehyde) believe it or not.