Adding sodium chloride to a saturated silver chloride solution lowers the silver chloride solubility because chloride is:

1. Both salts release the same ion into solution. 2. A saturated solution of silver chloride has its dissolution equilibrium established. 3. A common ion is one also produced by dissolution of the ionic compound. 4. Chloride from sodium chloride is exactly such an ion. 5. Compared with pure water, solubility is less in solutions containing a common ion. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 15 'Equilibria of Other Reaction Classes', sections 15.1-15.3_