$55.$ Flash distillation differs from fractional distillation in that:

$-$ A$)$ It requires a continuous feed

$-$ B$)$ It operates at multiple pressures

$-$ C$)$ It separates components in a single stage

$-$ D$)$ It produces a higher purity product

$56.$ The Fenske equation allows for the calculation of:

$-$ A$)$ Minimum reflux ratio

$-$ B$)$ Minimum number of theoretical stages at total reflux

$-$ C$)$ Heat duty required for reboiler

$-$ D$)$ Optimal feed stage location

$57.$ The Underwood equation is utilized to determine:

$-$ A$)$ The minimum reflux ratio for a given separation

$-$ B$)$ The total number of stages in a distillation column

$-$ C$)$ The distillate composition

$-$ D$)$ The maximum recovery of a distillate component

$58.$ Which of the following is true regarding total reflux in distillation?

$-$ A$)$ It indicates the column is operating without any distillate withdrawal

$-$ B$)$ It is the condition where the reflux ratio is minimized

$-$ C$)$ It represents the standard operating condition for industrial distillation columns

$-$ D$)$ It is achieved when the feed is introduced at the bottom of the column