* Porosity is the amount of empty space within a material.

Let's analyze each option:

* 1) Well-sorted fine-grained sediment: Fine-grained sediments like clay have small particles, which can pack together tightly, leaving less space for pores. However, being well-sorted means the particles are similar in size, which can lead to a lower porosity compared to poorly sorted sediment.

* 2) Coarse-grained: Coarse-grained sediments like gravel have larger particles, leaving more space between them, resulting in higher porosity.

* 3) Unfractured granite: Granite is a solid, igneous rock. Unfractured granite has essentially no pore space between its mineral crystals. This makes it the material with the lowest porosity.

* 4) Sand with well: Sand has moderate porosity, but the well would create a large open space, significantly increasing the overall porosity.

In summary: Unfractured granite, being a solid, dense material, has the lowest porosity compared to the other options.