Which ions are mostly soluble except for specific ions like Ba, Hg, and Pb?

Sulfates are generally soluble in water, with a few notable exceptions that include barium (Ba²⁺), mercury (Hg²⁺), and lead (Pb²⁺) sulfates. This solubility behavior is due to the nature of the sulfate ion (SO₄²⁻), which typically forms soluble compounds with most cations. However, when these specific cations are involved, the resulting sulfate compounds become insoluble.

The fact that barium sulfate, mercury sulfate, and lead sulfate are insoluble is attributed to the strong ionic lattice they form, which cannot easily dissociate into ions in aqueous solution. This characteristic makes sulfates distinct when considering solubility rules in chemistry, particularly regarding the exceptions involving heavy metals or ions from Group 2 of the periodic table.

In contrast, the other options, such as oxalates, chromates, and phosphates, have different solubility guidelines, with a broader range of insoluble behaviors across various cations, making them less representative of the stated query about solubility except for specific ions.