$5.$ In absorption column design, the height of a transfer unit $($HTU$)$ is important because:

$-$ A$)$ It directly relates to the column diameter.

$-$ B$)$ It indicates the efficiency of the solvent.

$-$ C$)$ It helps calculate the total height of the packed section.

$-$ D$)$ It determines the minimum solvent flow rate.

$6.$ Graphical methods for estimating the number of ideal stages in an absorption process are based on:

$-$ A$)$ The equilibrium curve and operating line.

$-$ B$)$ The solvent flow rate.

$-$ C$)$ The type of packing material.

$-$ D$)$ The temperature and pressure conditions.

$7.$ Analytical methods for determining the number of ideal stages usually involve:

$-$ A$)$ Calculating the HETP.

$-$ B$)$ Solving material balance equations.

$-$ C$)$ Determining the gas phase mass transfer coefficient.

$-$ D$)$ Measuring the liquid film thickness.

$8.$ The rate of absorption in a packed column can be affected by:

$-$ A$)$ The height of the column.

$-$ B$)$ The type of solvent used.

$-$ C$)$ The diameter of the packing material.

$-$ D$)$ All of the above.