Which of the following materials is considered unconfined formation?

The correct answer is sand, as it is classified as an unconfined formation in groundwater hydrology. Unconfined formations are typically characterized by layers of soil or gravel that allow groundwater to flow freely and be influenced directly by surface conditions. In the case of sand, it has high permeability, which allows water to seep through easily and maintain a close connection with the water table above.

In contrast, materials like cement, granite, and concrete do not allow for such effective water movement. Cement and concrete are both man-made materials used in construction that are impermeable and do not permit water to pass through. Granite, a type of igneous rock, is typically dense and has very low permeability, making it suitable as a confined formation where groundwater is not easily accessible. These characteristics differentiate sand as the only choice among the options that supports the concept of an unconfined aquifer.