Most of the movement in roots through apoplast is due to

The correct option is: "cortical cells are loosely packed and hence no resistance to water movement"

To understand why this is the correct answer, let us break down the mechanism of water movement in roots via the apoplast pathway:
The apoplast is the non-living system of cell walls and intercellular spaces in plant tissues through which water and solutes can move freely without crossing any cell membranes.

When water is absorbed by root hairs, it moves inward towards the vascular cylinder (xylem). In the root cortex, the cells (cortical cells) are very loosely packed with prominent intercellular spaces.
Because of this loose arrangement, water moving through the apoplast pathway encounters virtually no physical barrier or resistance in the cortex. It flows easily through the continuous network of cell walls and intercellular spaces of the cortical cells.

Once the water reaches the endodermis, however, its apoplastic movement is blocked by the suberized Casparian strips. But within the cortex itself, the loose packing of the cortical cells is the primary factor that facilitates rapid, low-resistance apoplastic water transport.