The correct option is C It is used by doctors for supporting fractured bones.
Plaster of Paris (CaSO4.0.5H2O) is a white powder which on mixing with water sets into hard solid mass due to formation of gypsum(CaSO4.2H2O).
CaSO4.0.5H2O+1.5H2O→CaSO4.2H2O
Therefore, Plaster of Paris is used for supporting fractured bones in the right position.
Washing soda is used for making glass, papers and soap.
Baking soda is used in soda-acid fire extinguisher.