Which of the following molecules do not exist?

Compound $X$ is the anhydride of sulphuric acid. The number of $\sigma$ bonds and the number of $\pi$ bonds present in $X$ are respectively:

The $P-P-P$ bond angle in $P_4$ and $S-S-S$ bond angle in cyclo $S_8$ molecule are respectively

For the following species,determine whether the octet rule is obeyed or not obeyed. Provide the reason for each:
$(1) BeF_4^{2-}$
$(2) BF_3$
$(3) CO_2$
$(4) NO$
$(5) NH_3$

In the electronic structure of acetic acid $(CH_3COOH)$,there are:

State the bond angle and bond length in ethene. What are the bond angles in $PCl_5$?