Which of the following molecules is theoretically not possible?

Which of the following facts is directly explained by the statement '$O$ is a smaller atom than $S$?'

Which of the following is an example of a super octet molecule?

Compare the $x$ and $y$ bond lengths in the following molecules:
Structure $1$: $HO-S(=O)-S(=O)-OH$ (where $x$ is the $S-S$ bond length)
Structure $2$: $HO-S(=O)_2-S(=O)-OH$ (where $y$ is the $S-S$ bond length)

In the trimer form of sulphur trioxide $(S_3O_9)$,each sulphur atom is bonded with:

The structure of $B_3N_3H_6$ (borazine) is as follows. How many derivative structures of $B_3N_3H_4X_2$ can be derived from the basic structure by the replacement of two hydrogen atoms?