NDA General Ability Question (2025) — Solution

Step-by-step solution

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. This statement is correct. The chemical formula of Plaster of Paris is CaSO_4 1 2 H_2O (calcium sulphate hemihydrate). The formula CaSO_4 2H_2O represents gypsum. Thus, this statement is incorrect. Washing soda (Na_2CO_3 10H_2O) is used for removing the permanent hardness of water by precipitating calcium and magnesium ions as insoluble carbonates. This statement is correct. The atmosphere of Venus is made up of thick white and yellow clouds of sulphuric acid. This statement is correct. Answer: The molecular formula of Plaster of Paris is CaSO_4 2H_2O