I believe it is element As, for arsenic.
This corresponds to the law of multiple proportions which states that when a certain amount of compound reacts to form another compound, the ratio of the amounts between the reactants and the products are a fraction of simple or whole numbers.<span />
Answer:
The structures are attached in file.
Hydrogen bonding and intermolecular forces is the reason for ranks allotted.
Explanation:
In determining Lewis structure, we calculate the overall number of valence electrons available for bonding. Making carbon (the least electronegative atom) the central atom in the structure, we allocate valence electrons until each atom has achieved stability.
In order of decreasing affinity to water molecules:

This is due to the fact that the
will accept protons more readily than the bicarbonate ion,
. Carbonic acid,
will not accept any more protons, hence it is the least attractive to water molecule, even though soluble.
The relationship of a pair of compounds could be one between these options :
- Structural isomerisms
happened when molecules with same molecular formula have bonded together in different orders
- Stereoisomerism
Happened when two or more compounds differing only in the spatial arrangement of their atom
hope this helps