Which one of the following compounds would undergo anionic polymerization at the fastest rate?

A student was preparing nitroethene from the reaction of nitromethane with formaldehyde in an acidic solution. In the workup step, they accidentally added a small excess of NaOH, resulting in a white coating on the inside wall of the reaction flask. What is the structure of the compound in the white coating?

A student was preparing nitroethene from the reaction of nitromethane with formaldehyde in an acidic solution. In the workup step, they accidentally added a small excess of NaOH, resulting in a white coating on the inside wall of the reaction flask. What is the structure of the compound in the white coating?