1. Alginate is

a. Reversible Hydrocolloid impression material

b. Irreversible Hydrocolloid impression material

c. Polysulfideimpression material

d. Polyvinyl siloxane impression material

Option b, Irreversible hydrocolloid impression material

Explanation:

Irreversible is used as an impression material to take impression from edentulous jaws. It is also used in wound healing and drug delivery.

Alginate is a natural polymer found in cell wall of brown seaweed.

Its monomers are β-D-mannuronate and α-L-guluronate.

In association with Ca2+, it forms gel. It is hydrophilic in nature.