Classification Nomenclature Isomerism

Plaster of Paris (POP) is chemically known as calcium sulphate hemihydrate. Its chemical formula is: It is obtained by heating gypsum (CaSO ·2H O) to about 373 K: This hemihydrate form sets into a hard mass when mixed with water, which is why it is used in casts, sculptures, and building materials.

The correct option is (D): calcium sulphate hemihydrate

The structure of the compound is CH₃–CH(Cl)–CH(Cl)–CH₃. This is a four-carbon straight chain alkane (butane) with chlorine atoms on the second and third carbon atoms. According to IUPAC naming conventions:

• The parent chain has 4 carbon atoms → butane
• Two chlorine substituents are attached → prefix "di" is used
• Their positions are on carbon 2 and 3 → locants are 2,3

The correct option is (C): 2, 3-dichlorobutane