Question

Which of the following statement is correct ?

• A. Sodium metal can be produced by the electrolysis of an aqueous solution of $NaCl$
• B. $CsOH$ has the maximum basicity and least solubility among all alkali metal hydroxides
• C. Gypsum when heated above $393K$ forms plaster of Paris
• D. The hydrated radii of alkaline earth metal ions decreases on moving down the group

Answer 1

The correct option is C Gypsum when heated above $393K$ forms plaster of Paris

• An aqueous solution of sodium chloride is not used for electrolysis because aqueous solution contains water as well which results in the formation of sodium hydroxide (NaOH) in the solution and sodium metal is not obtained.

• Among alkaline earth metal hydroxides, the anion being common, the cationic radius will influence the lattice enthalpy. Since lattice enthalpy decreases much more than the hydration enthalpy with increasing ionic size, the solubility increases down the group. Thus, CsOH is the most soluble alkali metal hydroxide.

• When Gypsum is warmed up to 393 K, it loses all its water and crystallises to give anhydrous calcium sulphate or calcium sulphate hemihydrate which is Plaster of Paris.

• The hydrated radii of alkaline earth metal ions increases on moving down the group because down a group, the number of energy levels (n) increases, so there is a greater distance between the nucleus and the outermost orbital. This results in a larger atomic radius.

Hence, option C is correct.