The plasticity index is the numerical difference between

ANS:A - liquid limit and plastic limit

1. Liquid Limit (LL): The liquid limit of a soil is the moisture content at which the soil transitions from a plastic state to a liquid state. It is determined by conducting the Casagrande's liquid limit test, where a soil sample is gradually mixed with water until it reaches a consistency where it just begins to flow along a groove of standard dimensions when jarred. The number of blows required to close a groove of standardized dimensions defines the liquid limit.
2. Plastic Limit (PL): The plastic limit of a soil is the moisture content at which the soil transitions from a plastic state to a semisolid state. It is determined by rolling a soil sample into a thread of uniform diameter. The soil is kneaded to form threads, and the moisture content at which the thread crumbles defines the plastic limit.