Which of the following pairs of canonical forms contribute equally to the resonance hybrid?

Compare the relative stability of the following resonating structures:

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:

$CH_2=CH-CH=CH-NH_3^+$ $(I)$
$^+CH_2-CH=CH-CH=NH_3^+$ $(II)$
$^+CH_2-CH=CH-CH=NH_3$ $(III)$
Which of these structures is not a valid canonical structure?

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

Which statement is true regarding the $PO_4^{3-}$ ion?
$A$. In $PO_4^{3-}$ ion,the $P-O$ bond order is $1.25$.
$B$. In $PO_4^{3-}$,the formal charge on each $O$ atom is $-0.75$.
$C$. $PO_4^{3-}$ shows four resonating structures.