$5.$ True$/$False: Three$-$phase flow involves the simultaneous flow of gas, liquid, and solid phases, making it significantly more complex than single or two$-$phase flows.

$6.$ True$/$False: Agitated vessels are typically used in gas$-$solid liquid systems to reduce mixing and mass transfer rates.

$7.$ True$/$False: The minimum fluidization velocity is the velocity at which all particles in a fluidized bed are suspended by the fluid flow.

$8.$ True$/$False: Bubble column reactors are primarily used for solid catalysis processes.