Q1: The minimum water content at which the soil just begins to crumble when rolled into threads 3 mm in diameter, is known

ANS:B - plastic limit

Plastic limit (Wp) is defined as the minimum water content at which soil begins to crumble when rolled into a thread of 3mm dia. The minimum water content at which the soil can be rolled into a thread of 3mm in diameter without crumbling. It's called THREAD TEST. Liquid limit - soil contain water with small shear strength.

Plastic limit -soil contain water in which the soil crumble into 3mm diameter.

Shrinkage limit-soil contains water 100%. It is fully saturated soil. From shrinkage limit the water content decrease.