The most mucostatic impression material is
Thin mix of plaster of paris
Zinc oxide eugenol impression paste
Free flowing wax
Reversible hydrocolloids
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