An isostere is

The option$(s)$ in which at least three molecules follow the Octet Rule is(are):
$(A)$ $CO_2, C_2H_4, NO$ and $HCl$
$(B)$ $NO_2, O_3, HCl$ and $H_2SO_4$
$(C)$ $BCl_3, NO, NO_2$ and $H_2SO_4$
$(D)$ $CO_2, BCl_3, O_3$ and $C_2H_4$

Considering ethene molecule,which of the following statements is/are correct?
$I$. $C-C$ bond is formed by overlapping of $sp^2-sp^2$ hybrid orbitals.
$II$. $C-H$ bond is formed by overlapping of $sp^2-s$ orbitals.
$III$. $p\pi-p\pi$ bond is present.
$IV$. $H-C-H$ bond angle is greater than $H-C-C$ bond angle.
$V$. Nodal plane of $\pi$ bond and molecular plane are same.

For the compound having the formula $GaAlCl_4$,the correct option from the following is:

The correct order of $S-S$ bond length in the following oxyanions is:
$(I) \, S_2O_4^{2-}$
$(II) \, S_2O_5^{2-}$
$(III) \, S_2O_6^{2-}$

Which of the following contains both covalent and ionic bonds?