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

Draw the resonance structures for the following compounds. Show the electron shift using curved-arrow notation.
$(a)$ $C_{6}H_{5}OH$
$(b)$ $C_{6}H_{5}NO_{2}$
$(c)$ $CH_{3}CH=CH-CHO$
$(d)$ $C_{6}H_{5}CHO$
$(e)$ $C_{6}H_{5}CH_{2}^{+}$
$(f)$ $CH_{3}CH=CH-CH_{2}^{+}$

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

During the formation of the dimer $N_2O_4$ from two molecules of $NO_2$,what happens to the unpaired electron on the nitrogen atom of each $NO_2$ molecule?

Explain the structure of $CO_{3}^{2-}$ ion in terms of resonance.

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