Which of the following compounds does not exhibit the resonance effect?

Which of the following structures represents the correct resonance structures of boron trifluoride $(BF_3)$?

The resonance hybrid of the nitrate ion $(NO_3^-)$ is represented as:

$A$ molecule may be represented by three structures having energies $E_1$,$E_2$ and $E_3$,respectively. The energies of these structures follow the order $E_3 < E_2 < E_1$. If the experimental bond energy of the molecule is $E_0$,the resonance energy is

$(i)$ Draw the resonance structures of $N_2O_3$ and state its shape.
$(ii)$ Indicate the bond angles and bond lengths in it.

Which of the following cannot be represented by resonance structures?