Who first provided an explanation for the formation of chemical bonds in terms of electrons?

Which of the following diagrams or statements is correct for the hybrid orbitals?

In which of the following compounds is the octet complete $(C)$ or incomplete $(IC)$ for all atoms?
$Al_2Cl_6$ $-$ $Al_2(CH_3)_6$ $-$ $AlF_3$ $-$ Dimer of $BeCl_2$ $-$ Dimer of $BeH_2$
(Note: $C$ for complete octet and $IC$ for incomplete octet.)

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

Identify the odd-electron molecules among $NO$,$NO_2$,$CO$,and $CO_2$. Explain why.

Chemical bond implies