Common salt, or sodium chloride (NaCl), is commonly used as a raw material in the preparation of various compounds. However, it is not used in the preparation of plaster of Paris.

1) Bleaching powder, also known as calcium hypochlorite (Ca(ClO)2), is prepared by reacting chlorine gas (Cl2) with slaked lime [Ca(OH)2]. Sodium chloride is not involved in this reaction.

2) Baking soda, or sodium bicarbonate (NaHCO3), is prepared from sodium chloride by the Solvay process. In this process, sodium chloride is reacted with ammonia (NH3) and carbon dioxide (CO2) to produce sodium bicarbonate.

3) Plaster of Paris, or calcium sulfate hemihydrate (CaSO4·0.5H2O), is not prepared using sodium chloride as a raw material. It is made by heating gypsum (calcium sulfate dihydrate, CaSO4·2H2O) to remove the water molecules, forming a fine white powder.

4) Washing soda, or sodium carbonate (Na2CO3), is also prepared by the Solvay process, which involves the reaction of sodium chloride with ammonia and carbon dioxide.

In summary