# If a compound is slightly soluble is it aqueous solution or solid?

If you're asking whether to write (aq) or (s) in a chemical reaction, it really depends on how much of it dissolves, which can be realized by calculating the solubility-product constant (${K}_{s p}$) of the compound's dissociation equation. A higher ${K}_{s p}$ indicates more of the dissociated ions are present, and is thus more soluble.
Some textbooks say they write (aq) instead of (s) if the solubility is greater than $0.01 \frac{g}{L}$, but it's merely arbitrary. Your best bet would be to refer to a solubility guidelines/chart to determine which are soluble and insoluble. (The term "insoluble" is not very practical, as all ionic compounds are soluble to some extent (calculated via ${K}_{s p}$), but they generally call a compound "insoluble" if the solubility guidelines say so, i.e. you would maybe write (s) in the reaction.)