$17.$ An optimum reflux ratio seeks to $\_\_$ between capital and operational costs, achieving an economical balance for $\_\_$ while maintaining $\_\_\_\_.$

$18.$ Relative volatility measures the ease of separating a mixture by distillation and is defined by the ratio of $\_\_$ of the components, crucial for $\_\_$ and $\_\_\_\_$ design.

$19.$ In flash distillation, a $\_\_$ feed results in $\_\_$ and phases in equilibrium at a specific and $\_\_\_\_.$

$20.$ Total reflux in distillation operations means no $\_\_$ is withdrawn, and the process is used to establish $\_\_$ requirements and $\_\_\_\_$ configurations...