The correct stability order of the following resonance structures of $CH_3-CH=CH-CHO$ is:

The correct stability order of the following resonance structures is:

Resonance structures of propenal are given below. Which of these resonating structures is more stable? Give reason for your answer.
$CH_2=CH-CH=O$ $(I)$ $\leftrightarrow$ $\stackrel{+}{CH_2}-CH=CH-\stackrel{-}{O}$ $(II)$

The relative stability of the contributing structures is:

Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation.
$(a)$ $C_{6}H_{5}OH$
$(b)$ $C_{6}H_{5}NO_{2}$
$(c)$ $CH_{3}CH=CH-CHO$
$(d)$ $C_{6}H_{5}CHO$
$(e)$ $C_{6}H_{5}CH_{2}^{+}$
$(f)$ $CH_{3}CH=CH-CH_{2}^{+}$

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