Which one of the following statements is NOT correct ?

Statement 2 is incorrect because the molecular formula of Plaster of Paris is Calcium Sulphate Hemihydrate (CaSO4·1/2H2O), not CaSO4·2H2O [1]. The formula CaSO4·2H2O actually represents Gypsum, which is a hard solid mass formed when Plaster of Paris reacts with water [1]. Water of crystallization is correctly defined as the fixed number of water molecules present in one formula unit of a salt [1]. Washing soda (sodium carbonate) is widely used in industrial and domestic applications for removing the permanent hardness of water caused by calcium and magnesium salts. Additionally, the atmosphere of Venus is indeed characterized by thick, reflective clouds composed primarily of sulphuric acid droplets, which contribute to its high albedo and extreme greenhouse effect. Therefore, the only false statement among the options is the molecular formula provided for Plaster of Paris.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Plaster of Paris > p. 33