$44.$ The Height Equivalent to a Theoretical Plate $($HETP$)$ in packed column design is a critical parameter because it reflects:

$-$ A$)$ The maximum flow rate of gas the column can handle.

$-$ B$)$ The efficiency of the packing material in promoting mass transfer.

$-$ C$)$ The chemical resistance of the packing material to the solvent.

$-$ D$)$ The total weight of the packing material required.

$49.$ The choice of solvent in a gas absorption process affects the column design primarily through its:

$-$ A$)$ Cost and availability.

$-$ B$)$ Impact on NTU and HTU, thereby influencing the efficiency and height of the column.

$-$ C$)$ Color and odor, which may affect environmental and safety regulations.

$-$ D$)$ Boiling point and freezing point, which determine operational temperature ranges.

$50.$ When estimating the number of ideal stages using graphical methods, the slope of the operating line is crucial because it:

$-$ A$)$ Directly relates to the gas flow rate to solvent flow rate ratio, impacting the efficiency of separation.

$-$ B$)$ Indicates the thermal stability of the solvent.

$-$ C$)$ Determines the minimum size of the packing material.

$-$ D$)$ Affects the choice of materials for constructing the column.

$51.$ The rate of absorption in a packed tower is a function of:

$-$ A$)$ The solvent flow rate exclusively.

$-$ B$)$ The gas and solvent flow rates, as well as the mass transfer coefficients.

$-$ C$)$ The diameter of the tower.

$-$ D$)$ The type of gas being absorbed$.$