A pycnometer is used to determine

ANS:C - water content

Water content refers to the amount of water present in a substance or material, usually expressed as a percentage of the total mass or volume of the material. In soil mechanics, water content specifically refers to the proportion of water in a soil sample relative to the total mass of the soil. It is a critical parameter because it affects the behavior, strength, and engineering properties of the soil. Water content is determined through laboratory tests and is essential for soil classification, compaction, permeability, drainage, and shear strength analysis in engineering and construction projects.