The water content of soil, which represents the boundary between plastic state and liquid state, is known as A. liquid limit B. plastic limit C. shrinkage limit D. plasticity index

The correct answer is A. liquid limit.

The liquid limit is the water content of soil at which it will flow under its own weight. It is determined by the Atterberg limits test, which is a series of tests used to determine the consistency of fine-grained soils. The other options are incorrect because:

• The plastic limit is the water content of soil at which it will just begin to crumble when rolled into a thread 1/8 inch in diameter.
• The shrinkage limit is the water content of soil at which it will no longer shrink when dried.
• The plasticity index is the difference between the liquid limit and the plastic limit. It is a measure of the plasticity of the soil.