ANS:D - both (b) and (c)

Channelling in a packed tower, which refers to the formation of preferential flow paths through the packing material, can result from both the maldistribution of liquid and the non-uniformity of packing.

• Maldistribution of liquid: When the liquid flowing through the packed tower is not evenly distributed across the cross-section of the tower, certain areas may receive more liquid than others. This uneven distribution can lead to channelling, where the liquid preferentially flows through specific pathways, bypassing other regions of the packing material.
• Non-uniformity of packing: If the packing material is not uniformly distributed or if there are irregularities in its geometry or arrangement, it can create pathways of least resistance for the liquid to flow through. These preferential flow paths can also lead to channelling, as the liquid tends to follow the easier routes through the packing.