<prompt> The impression material that is mainly composed of sodium or potassium salts of alginic acid is ___.PolyetherIrreversible hydrocolloidPolyvinyl siloxanePolysulfide  <response>: Irreversible hydrocolloid IH or alginate is the material of choice to produce diagnostic casts. Its composition is mainly sodium or potassium salts of alginic acid. They react chemically with calcium sulfate to produce insoluble calcium alginate. 