The most mucostatic impression material is
(A) Thin mix of plaster of paris (B) Zinc oxide eugenol impression paste (C) Free flowing wax (D) Reversible hydrocolloids
(A) Impression plaster is a β-calcium sulfate hemihydrate used at a water/powder ratio of approximately 0.5 to 0.6. Its fluidity makes it suitable for making impressions of soft tissues in the uncompressed state, a characteristic of mucostatic impression material.
Rest all options are mucocompressive impression materials.
Ref: Phillips 12edition page no 177