The correct answer is A. 0 < PI < 7.
The plasticity index (PI) is a measure of the range of water contents over which a soil will exhibit plastic behavior. It is defined as the difference between the liquid limit (LL) and the plastic limit (PL). Soils with a PI of 0 to 7 are considered to be of low plasticity, soils with a PI of 7 to 17 are considered to be of medium plasticity, and soils with a PI of greater than 17 are considered to be of high plasticity.
The liquid limit (LL) is the water content at which a soil will flow under a standard shear stress. The plastic limit (PL) is the water content at which a soil will just begin to crumble when rolled into a thread 1/8 inch in diameter.
The plasticity index is an important parameter in soil mechanics because it is used to classify soils and to determine their engineering properties. Soils with a high PI are more difficult to work with and are more likely to be unstable.