Which of the following is not a pair of resonating structures?

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 $X: 3, Y: 2$.

Resonance structures can be written for

For which of the following can resonance structures be drawn? Why?
$CO_2, NO_2, O_3, O_2, CH_4$

Although $ClO_2$ is an odd-electron molecule,it does not dimerize because...

The correct order of $Cl-O$ bond order is