Question

now, lets take a look at another molecule to determine if it will dissolve in water. in other words, will water molecules form a hydration sphere around this molecule?
the molecule on the right is iodine (i₂). it is found in foods, such as seaweed, and is required by the human body, especially the thyroid gland.
why do you think iodine is insoluble in water?
iodine is a positive ion, so it wont dissolve in water.
iodine is a negative ion, so it wont dissolve in water.
iodine has both a full positive charge and a full negative charge, so it will not dissolve in water.
iodine is held together with strong covalent bonds and lacks any significantly charged regions. the interactions between water and iodine are not strong enough to overcome these covalent bonds.
molecules of iodine are made up of more than one atom.

Explanation:

Water is a polar molecule (has charged regions due to uneven electron sharing in its \(H - O\) bonds). For a substance to dissolve well in water (form a hydration sphere), it should have some polarity or charged regions to interact with water's polar regions (through dipole - dipole or ion - dipole interactions).
Iodine (\(I_2\)) is a non - polar molecule. The two iodine atoms in \(I_2\) share electrons equally (covalent bond) and there are no significantly charged regions. The covalent bonds within \(I_2\) are strong, and the only interactions between \(I_2\) and water would be weak London dispersion forces. These weak forces are not strong enough to break the covalent bonds in \(I_2\) and allow it to dissolve (i.e., form a stable hydration sphere).
The first two options are wrong because \(I_2\) is not an ion. The third option is wrong as \(I_2\) has no full positive and negative charges. The fifth option is incorrect because the number of atoms in a molecule (as long as it's a covalent molecule) is not the reason for solubility in water (for example, \(CO_2\) has 3 atoms but is more soluble than \(I_2\) in water due to its polar nature).

Answer:

Iodine is held together with strong covalent bonds and lacks any significantly charged regions. The interactions between water and iodine are not strong enough to overcome these covalent bonds.