There are solubility rules and for soluble compounds some have exceptions next to them.
Such as Halides are soluble
Exception: Ag, Hg, Pb
What does it mean by exception?
For Halides would it be, that if the compound was AgCI it wouldn't be soluble?
Right. AgCl, Hg2Cl2, and PbCl2 are not soluble. The other chlorides are. For whatever it's worth, PbCl2 is soluble in hot water but not cold water.
In the context of solubility rules, an "exception" refers to a specific condition or case where a general rule does not apply. When it comes to the solubility of halides, the general rule states that most halides are soluble in water. However, there are certain exceptions to this rule.
In the case of Ag (silver), Hg (mercury), and Pb (lead), their halide compounds have low solubility and are often considered insoluble. Therefore, if you have a compound like AgCl (silver chloride), it would be an exception to the general rule, and it would indeed be considered insoluble or slightly soluble in water.
These exceptions are important to note because they allow you to understand the limits of the general solubility rule. By presenting the exceptions next to the general rule, you can ensure that you are aware of specific cases where the rule does not apply and adjust your understanding accordingly.