$CH_3-C(=O)-OCH_3$. In the given structure,the bond between carbonyl carbon and oxygen is $a$ and the bond between oxygen and methyl group is $b$. The correct relation between the bond lengths $a$ and $b$ is:

Resonance in $X_2Y$ can be represented as shown in the image. The enthalpy of formation of $X_2Y$ $(X \equiv X(g) + \frac{1}{2} Y = Y(g) \rightarrow X_2Y(g))$ is $80 \ kJ \ mol^{-1}$. The magnitude of resonance energy of $X_2Y$ is $......... \ kJ \ mol^{-1}$ (nearest integer value). Given: Bond energies of $X \equiv X, X=X, Y=Y$ and $X=Y$ are $940, 410, 500$ and $602 \ kJ \ mol^{-1}$ respectively. Valence $X: 3, Y: 2$.

What are the characteristics of resonance structures?

What is the difference between the resonance structures of $CH_3CH_2COO^{-}$ and $CH_3COOH$?

Compare the relative stability of the following resonating structures:
$(i)$ $CH_3-CH=C(CN)-COCH_3$
(ii) $CH_3-CH=C(CN)-C^+(O^-)CH_3$
(iii) $CH_3-C^+(H)-C(CN)=C(O^-)CH_3$
(Note: The structures are provided in the image.)

Which of the following pairs are not resonating structures?