$5.$ The $\_\_\_\_\_\_\_\_\_\_$ extraction method involves the solvent and feed moving in the same direction, which can lead to less efficient separation compared to the $\_\_\_\_\_\_\_\_\_\_$ method.

$6.$ Counter$-$current extraction increases separation efficiency by allowing the solvent and the feed to move in $\_\_\_\_\_\_\_\_\_\_$ directions, maximizing contact time and equilibrium stages.

$7.$ When choosing solvents for extraction, their $\_\_\_\_\_\_\_\_\_\_$ with each other is crucial to avoid the formation of azeotropes, which can complicate the recovery process.

$8.$ The use of $\_\_\_\_\_\_\_\_\_\_$ solvents in extraction is favored when the components have similar physical properties but can be selectively dissolved.