Dissolution value is the molar solubility of the substance which is the molar concentration of a saturated solution. This is calculated from the
Let's say you have a solid that is dissolving
So in your example
The dissolution value will be the concentration of the chromate ion (this will also be the concentration of the solution). Each formula unit of the compound dissociates into 2 silver ions and 1 chromate ion so the concentration of silver ions will be double that.