Correct option is D
The cohesive index property of soils reflects the behavior of fine-grained (cohesive) soils, especially clays, in terms of their consistency and plasticity.
Atterberg limits (Liquid Limit, Plastic Limit, and Plasticity Index) are the standard index properties used to identify and classify cohesive soils and to assess their engineering behavior.
Why other options are incorrect
(A) In-place density → A state property, not an index property of cohesion.
(B) Shape of particles → More relevant to coarse-grained soils.
(C) Clay content → Indicates presence of clay but is not an index property used for classification.
Hence, the correct option is (D).
