How many resonance structures are there for anthracene?

Caliene,$C_7H_6$,is expected to be a fairly polar aromatic molecule. Which of the following resonance forms contributes to the greatest extent towards the real structure (resonance hybrid) of the molecule?

The increasing order of stability of the resonance structures is:

The acetate ion $(CH_3COO^-)$ contains:

In the given $HNO_3$ molecule,identify the bond lengths $a$ and $b$ (where $a$ and $b$ are bond lengths).

Given that:
$(i) \Delta_f H^o$ of $N_2O$ is $82 \ kJ \ mol^{-1}$
$(ii)$ Bond energies of $N \equiv N, N = N, O = O$ and $N = O$ are $946, 418, 498$ and $607 \ kJ \ mol^{-1}$ respectively.
The resonance energy of $N_2O$ is $...... \ kJ \ mol^{-1}$.