ANS:C - repeated coalescence & redispersion of the drop phase.

Perforated plate towers are commonly used in solvent extraction processes for several reasons:

1. Higher Contact Area: Perforated plates provide increased surface area for contact between the phases (typically a solvent and a feed solution or extractant). The perforations create numerous contact points where mass transfer can occur, enhancing the efficiency of the extraction process.
2. Better Contact of the Phases: The design of perforated plates allows for intimate contact between the solvent and the feed solution. This close contact facilitates mass transfer between the phases, ensuring efficient extraction of the desired components.
3. Repeated Coalescence and Redispersion of the Dispersed Phase: Perforated plates can induce turbulence and mixing in the system, leading to repeated coalescence and redispersion of the dispersed phase (such as droplets of solvent or extractant). This enhances mass transfer by continuously exposing fresh interface between the phases, promoting extraction efficiency.