What is the bond order of the carbon-carbon bond in benzene?

Which of the following is the most unstable resonating structure of phenol?

Draw different resonance structures of the following:
$(a)$ $CH_3COO^{-}$
$(b)$ $CH_2=CH-CHO$
$(c)$ Aniline $(C_6H_5NH_2)$
$(d)$ $C_6H_5NO_2$
$(e)$ Phenol

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

With respect to resonance structures of $CO_3^{2-}$ ion, which of the following statements are correct?
$(a)$ All $C – O$ bonds in $CO_3^{2-}$ are equivalent
$(b)$ There are three resonance structures possible for $CO_3^{2-}$ ion
$(c)$ The position of carbon and oxygen should change in every resonance structure
$(d)$ The formal charge on carbon atom is $0$

Resonance is due to