Which of the following cannot act as a Lewis base?

The single,double and triple bond lengths of carbon in carbon dioxide are respectively

Select the correct order:
$(a)$ $CO < CO_2 < CO_3^{2-}$ $\Rightarrow$ Bond length
$(b)$ $O_2 < O_3 < O_2^{2-}$ $\Rightarrow$ Bond length
$(c)$ $N_2 < N_2^+$ $\Rightarrow$ Bond energy

Which one of the following molecules contains no $\pi$ bond?

Which of the following molecules has a central atom with a complete octet?

The Born-Haber cycle can be used to estimate: