ANS:A - Packed column (with stacked packing)

Among the options provided, the column that typically incurs the lowest pressure drop is the bubble plate column. Bubble plate columns, also known as tray columns, utilize perforated plates with bubble caps or sieve holes to facilitate contact between the gas and liquid phases. This design allows for efficient mass transfer while minimizing pressure drop. Here's why bubble plate columns generally have lower pressure drops compared to the other options:

1. Bubble Plate Design: Bubble plates provide a structured surface for the liquid to spread out evenly across the tray while allowing gas to bubble up through the liquid. This design promotes efficient contact between the gas and liquid phases, leading to effective mass transfer with relatively low resistance to flow.
2. Stacked Packing in Packed Columns: Packed columns with stacked packing typically have higher pressure drops compared to bubble plate columns. Stacked packing materials, such as structured packing or random packing, offer a large surface area for mass transfer but can create significant resistance to flow due to the tortuous paths the gas and liquid must follow through the packing material.
3. Dumped Packing in Packed Columns: Packed columns with dumped packing also tend to have higher pressure drops compared to bubble plate columns. Dumped packing materials, such as random dumped packing or structured dumped packing, can create high turbulence and interfacial area for mass transfer but may result in higher pressure drops due to the irregular packing arrangement.
4. Pulse Column: Pulse columns utilize pulsed gas or liquid flows to enhance mass transfer. While pulse columns can offer advantages in terms of mass transfer efficiency, they may not necessarily have lower pressure drops compared to bubble plate columns, especially depending on the specific operating conditions and design considerations.