In a saturated solution of electrolytes, the ionic products of their concentration are constant at a particular temperature. This constant for an electrolyte is known as:
(A) Ionic product
(B) Ionisation constant
(C) Dissociation Constant
(D) Solubility product

Hint: The ionic products of their concentration are assumed to be constant in this question, thus we must explain what the constant for an electrolyte is called. There are many different types of phrases used in the solution; initially, we must comprehend every term before we can finish the entire answer.

Complete step by step solution:
Prior to beginning the solution, it is important to understand that equilibrium has been reached when the rates of the forward and reverse reactions are equal. Each reactant and product concentrations are constant at equilibrium.
As we also know, the equilibrium constant for a chemical reaction in which a solid ionic molecule dissolves to create its ions in solution is called the solubility product.
In order to estimate,
$CuS{O_4}(s)\overset {} \leftrightarrows C{u^{2 + }} + S{O_4}^{2 - }$
For above-equilibrium, the solubility product is given below,
${K_{sp}} = [C{u^{2 + }}][S{O_4}^{2 - }]$
Where $[C{u^{2 + }}]$ and $[S{O_4}^{2 - }]$ are ion concentrations that $CuS{O_4}$ has dissociated into.
Therefore, the correct answer is Solubility Product.

Additional Information :
Solubility is defined as the property of a substance known as solute to get dissolved in a solvent for the formation of a solution. The solubility of ionic compounds that dissociate and form cations and anions in water varies to a great extent. Some compounds are highly soluble and can even absorb moisture from the atmosphere whereas, on the other hand, the others are highly insoluble.

Hence, the correct option is (D)

Note: The equilibrium solubility of an additive in a polymer is the most important physical property of the system because it determines how much of the additive can be present in the polymer as a homogeneous solution.