Permeability refers to the ability of a material to allow fluids (like water) to pass through it.

Sand has larger particle sizes and more space between the particles, creating larger pores. These larger pores allow water to flow through the sand more easily.

Clay pebbles have smaller particle sizes and less space between the particles, resulting in smaller pores. This makes it harder for water to pass through clay pebbles.

In summary:

* Sand: High permeability due to larger pores.

* Clay pebbles: Low permeability due to smaller pores.

Therefore, sand is more permeable than clay pebbles.