Resonating structures have different

Point out the incorrect statement about resonance.

Resonance structures can be written for

Identify the relationship between the following two structures: $\begin{matrix} \overset{\Theta}{\overset{\centerdot \,\centerdot}{C}}H_2-C(=O)-CH_3 \end{matrix}$ and $\begin{matrix} CH_2=C(O^{\Theta})CH_3 \end{matrix}$

Explain the important aspects of resonance with reference to the $CO_{3}^{2-}$ ion.

$CH_2=CH-CH=CH-NH_3^+$ $(I)$
$^+CH_2-CH=CH-CH=NH_3^+$ $(II)$
$^+CH_2-CH=CH-CH=NH_3$ $(III)$
Which of these structures is not a valid canonical structure?