Under what conditions can resonance structures be drawn?

The most unlikely representation of resonance structures of $p-$nitrophenoxide ion is

Which of the following pairs are not resonating structures?

$CH_3-C(=O)-OCH_3$. 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:

Which of the following statements are true for the nitrate ion $(NO_3^-)$?
$(a)$ The coordination number of $N$ is $3$,and the structure is trigonal planar.
$(b)$ The formal charge on $N$ is $+1$.
$(c)$ The average formal charge on each $O$ atom is $-2/3$.
$(d)$ The average bond order of the $NO$ bond is $4/3$.
$(e)$ All $NO$ bond lengths are identical due to resonance.
Select the correct code:

During the formation of the dimer $N_2O_4$ from two molecules of $NO_2$,the odd electron on the nitrogen atom of each $NO_2$ molecule pairs up. What is the resulting structure?