$12.$ For a solvent to be considered effective in an extraction process, it must have a high selectivity and affinity towards the solute, which is often measured by the $\_\_\_\_\_\_\_\_\_\_.$

$13.\_\_\_\_\_\_\_\_\_\_$ phase diagrams are essential tools for visualizing the solubility and miscibility of three$-$component systems and guiding the selection of extraction solvents.

$14.$ The choice between using miscible or immiscible solvents in an extraction process depends on the nature of the feed and the desired $\_\_\_\_\_\_\_\_\_\_$ of the final product.

$15.$ In solvent recovery, the aim is to $\_\_\_\_\_\_\_\_\_\_$ the used solvent for reuse in the process, which is essential for economic and environmental sustainability.