Final answer:
To assess if a solution is stable or unstable, conducting a stability test is most appropriate. This involves determining if the identity of the substance has changed, which indicates chemical stability.
Step-by-step explanation:
To tell if a solution is stable or unstable, one should perform a stability test rather than solely relying on color change, pH measurement, or conducting a solubility test. A stability test can determine if the identity of a substance has changed, indicating a chemical change and therefore stability or instability of a solution. Additionally, determining if a precipitate forms during a reaction can indicate a chemical change, such as the formation of barium sulphate, which can be identified using a specific test for its presence. The pH of a solution can indicate its acidic or basic nature and can be estimated using colored indicators or pH paper, but this is not a direct measure of stability. Solubility tests can show how substances dissolve in water, but do not directly assess stability unless the solubility characteristics are pertinent to the solution's intended use or stability parameters.