What is the correct increasing order of $C-O$ bond length in $CO$,$CO_3^{2-}$,and $CO_2$?

Which of the following cannot be represented by resonance structures?

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 $0$

Use the following data to answer the question below.
Calculate the resonance energy of anthracene in $kcal/mol$.

What is resonance energy? Write about its value.

What points should be kept in mind while drawing resonance structures?