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

Compare $\pi$-bond strength between $B$ and $N$ in the following compounds: $(I)$ $((CH_3)_3Si)_2N^{-}BH_2$ and $(II)$ $((CH_3)_3C)_2N^{-}BH_2$.

In how many isomeric forms does $B_3N_3H_4Cl_2$ exist?

In the $Al_2Cl_6$ dimer,which of the following statements is true regarding the $Al-Cl$ bonds?

Select the incorrect statement about $N_2F_4$ and $N_2H_4$ :
$(I)$ In $N_2F_4$,$d$-orbitals are contracted by electronegative fluorine atoms,but $d$-orbital contraction is not possible by $H$ atoms in $N_2H_4$.
$(II)$ The $N-N$ bond energy in $N_2F_4$ is more than the $N-N$ bond energy in $N_2H_4$.
$(III)$ The $N-N$ bond length in $N_2F_4$ is more than that in $N_2H_4$.
$(IV)$ The $N-N$ bond length in $N_2F_4$ is less than that in $N_2H_4$.
Choose the correct code:

What are the formal charge on each oxygen atom and the $P-O$ bond order in the $PO_4^{3-}$ ion,respectively?