$9.$ Batch contact extractors are characterized by their $\_\_\_\_\_\_\_\_\_\_$ operation, where the solvent and feed are mixed and then allowed to settle for phase separation.

$10.$ Continuous contact extractors, such as the $\_\_\_\_\_\_\_\_\_\_$ extractor, are preferred for large$-$scale operations due to their ability to handle large volumes of feed continuously.

$11.$ The effectiveness of solvent extraction can be quantified by the $\_\_\_\_\_\_\_\_\_\_$ coefficient, which measures the distribution of a solute between two immiscible solvents.

$12.$ 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 $\_\_\_\_\_\_\_\_\_\_.$