The impression material with lowest viscosity is: (A) Plaster of paris, (B) Agar-agar, (C) Zinc oxide eugenol, (D) Elastomers
Answer is 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.
Ref: Phillips 12 ed page no 177