The resonance energy of the following heterocycles is in the order:

How many resonance forms can be written for the nitrate ion,$(NO_3^-)$?

Which of the following species has all bond angles equal to $120^o$ and all bond lengths equal?

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 $X: 3, Y: 2$.

Consider the following three resonance structures:
The correct order of their stabilities is:

Which of the following cations is more stable?