ANS:A - incurs smaller pressure drop.

Let's break down the advantages of a packed tower compared to a plate tower for a particular mass transfer operation:

1. Smaller Pressure Drop: A packed tower typically incurs a smaller pressure drop compared to a plate tower. This is because in a packed tower, the gas and liquid flows through a bed of packing material, which offers less resistance compared to the flow through trays or plates with perforations.
2. Allows Installation of Cooling Coils: Packed towers offer more flexibility for the installation of additional equipment, such as cooling coils, because the packing material provides a larger surface area and void space compared to trays or plates. This allows for better integration of auxiliary equipment for controlling temperature or other process parameters.
3. Less Costly in Large Sizes/Diameters: Packed towers tend to be less costly when built in large sizes or diameters compared to plate towers. This is because the construction of packed towers involves stacking packing material, which can be more economical than fabricating and installing multiple trays or plates with complex internals.
4. More Suitable if Suspended Solids are Present: Packed towers are generally more suitable if suspended solids are present in fluid streams. The packing material helps to retain solids and prevent them from accumulating on trays or plates, which can lead to fouling and reduced efficiency in plate towers.

So, considering these advantages, we can conclude that a packed tower is typically preferred over a plate tower for a particular mass transfer operation, especially when factors such as pressure drop, flexibility for additional equipment, cost-effectiveness in larger sizes, and handling of suspended solids are important considerations.