The following tables give the solubility rules for some common solids at room temperature. If a solid has a minimum solubility of 0.1 mole per litre of solution at room temperature, it is regarded as a soluble solid. If the solubility is less than 0.001 mole per litre at room temperature it is regarded as insoluble solid. Solubility lying between 0.001 to 0.1 mole per litre comes under slightly soluble category. In the following tables slightly soluble solids(eg. CaSO~4~, PbCl~2~, PbBr~2~ etc.) have been kept under insoluble category. N.B: Actually there is nothing like insoluble substances. They are actually *sparingly soluble*. For lower school level, we regard them as insoluble for writing ionic equations.) **Solubility Rules(Table-I)** | (A) Soluble Category | Exceptions:(Insoluble) | | :---- | :----| | 1. Inorganic acids **(ALL)** (HCl, H~2~SO~4~, HNO~3~ etc.) | _ | | 2.alkali metal (Li^+^, Na^+^, K^+^ , Rb^+^, Cs^+^,