Which of the following pairs of molecules contains an odd-electron molecule and an expanded octet molecule?

The total number of lone pairs of electrons in melamine is

Fill in the blanks:
$(i)$ In $1927$,Heitler and London proposed the ........ theory.
$(ii)$ The ${\rm{ClF}}_3$ molecule has a .... shape.
$(iii)$ The number of bonding pairs in ions with a square planar shape is .......... .
$(iv)$ The value of the dipole moment in ${\rm{HBr}}$ is .......... .

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 $N_2$

$X-O-X$ linkage is present in $[X = P/S/Cl/Mn]$:
$(a) P_2O_7^{4-}$
$(b) S_2O_5^{2-}$
$(c) S_2O_7^{2-}$
$(d) Cl_2O_7$
$(e) Mn_2O_7$
$(f) S_2O_8^{2-}$

Which of the following pairs are isostructural?