$5.$ Which phase combination is involved in a three$-$phase flow?

A$.$ Gas only

B$.$ Liquid only

C$.$ Gas, liquid, and solid

D$.$ Gas and two different liquids

$6.$ In the context of gas$-$solid liquid reactors, what does a "packed bed" refer to$?$

A$.$ A reactor filled with fluid only

B$.$ A column packed with solid particles

C$.$ A bed for gas storage

D$.$ A liquid phase with high viscosity

$7.$ What is the minimum fluidization velocity?

A$.$ The velocity at which solid particles begin to settle

B$.$ The velocity at which all solid particles are suspended by the fluid

C$.$ The maximum velocity of the fluid without causing erosion

D$.$ The velocity at which phase separation occurs

$8.$ Which of the following best describes a bubble column reactor?

A$.$ A column filled with packed solids

B$.$ A reactor utilizing high$-$speed jets

C$.$ A vessel in which gas bubbles rise through a liquid

D$.$ A system designed for solid catalysis