Which of the following species exists?

Number of $\pi$ electrons in cyclobutadienyl anion $({C_4}{H_4})^{2-}$ is

The correct order of strength of $\pi-$ bond$(s)$ is:
$I$. $BO_3^{-3} < CO_3^{-2} < NO_3^{-}$
$II$. $ClO_4^{-} > SO_4^{-2} > PO_4^{-3}$
$III$. $BF_3 > BCl_3 > BBr_3$
$IV$. $AlCl_3 < BCl_3$

Identify the odd-electron molecules among $NO$,$NO_2$,$CO$,and $CO_2$. Explain why.

Select the pair of compounds in which both have different hybridization but have the same molecular geometry.

Identify the correct orders against the property mentioned:
$(A)$ $H_2O > NH_3 > CHCl_3$ - dipole moment
$(B)$ $XeF_4 > XeO_3 > XeF_2$ - number of lone pairs on central atom
$(C)$ $O-H > C-H > N-O$ - bond length
$(D)$ $N_2 > O_2 > H_2$ - bond enthalpy
Choose the correct answer from the options given below: