Final answer:
A saturated solution of a slightly soluble electrolyte is in equilibrium when the rate of dissolution equals the rate of precipitation, establishing a dynamic balance. This is termed a heterogeneous equilibrium because b. it involves multiple phases: the solid electrolyte and the aqueous solution with dissolved ions.
Step-by-step explanation:
A saturated solution of a slightly soluble electrolyte in contact with some of the solid electrolyte is said to be a system in equilibrium because there is a constant rate of the dissolution and precipitation processes. The dissolved ions in the saturated solution are in dynamic balance with the solid phase, meaning that the rate at which the solid dissolves to form ions is equal to the rate at which ions combine to form the solid.
This situation is called a heterogeneous equilibrium because it involves multiple phases: the solid electrolyte and the ionized form in solution.
The correct answer to why such a system is called a heterogeneous equilibrium is (b) It involves multiple phases. This involves the solid phase of the undissolved electrolyte and the aqueous phase where the ions are dissolved.