Back bonding in $BF_3$ does not affect

Identify the correct statement$(s)$ from the following:
$a$) Dipole moment of $NH_3$ is more than $NF_3$
$b$) $SF_4$ is square planar
$c$) $SnCl_4$ is more covalent than $SnCl_2$
$d$) $In_2SO_4$ sulphur atom has expanded octet

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:

Identify the statement$(s)$ which is(are) not correct from the following:
$a)$ $NH_3$ and $H_3O^+$ are isostructural
$b)$ $ClF_3$ has $T$-shape
$c)$ $O_2$ molecule is paramagnetic
$d)$ Bond order of $N_2^+$ is more than $N_2$

In the solid state,$PCl_5$ exists as which of the following?

The correct order of increasing bond length of $C - H, C - O, C - C$ and $C=C$ is